rune/libenclave/pal: Reformat PAL API spec

Reformat spec_v1.md and spec_v2.md
Signed-off-by: NShirong Hao <shirong@linux.alibaba.com>

rune/libenclave/internal/runtime/pal/spec_v1.md

-# Enclave Runtime PAL API Specification
+# Enclave Runtime PAL API Specification v1
 Enclave Runtime PAL API defines a common interface to interact between `rune` and enclave runtime.
 
-## pal_init()
-| **Description** | Initialize enclave runtime with specific attributes. |
-| :-: | :- |
-| **Prototype** | struct pal_attr_t {<br/>      const char \*args;<br/>      const char \*log_level;<br/>};<br/>int pal_init(const struct pal_attr_t *attr); |
-| **Parameters** | @args: the enclave runtime specific argument string.<br/>@log_level: the output log level of enclave runtime. |
-| **Return value** | 0: Success<br/>-ENOENT: Invalid instance path of enclave runtime<br/>Others: Enclave runtime specific error codes |
-
-## pal_exec()
-| **Description** | Pass the path of the application to be executed, and synchronously wait for the end of the application to run and return the result. |
-| :-: | :- |
-| **Prototype** | struct pal_stdio_fds {<br/>      int stdin, stdout, stderr;<br />};<br/>int pal_exec(char \*path, char \*argv[],<br/>             struct pal_stdio_fds \*stdio,<br/>             int \*exit_code); |
-| **Parameters** | @path: The path of the application to be run<br/>@argv: The array of argument strings passed to the application, terminated by a NULL pointer<br/>@stdio: The stdio fds consumed by the application<br/>@exit_code: Return the exit code of an application |
-| **Return value** | 0: success<br/>-ENOENT: The path does not exist<br/>-EACCES: Permission denied<br />-ENOEXEC: The path is not an executable file<br =/>-ENOMEM: <br />-EINVAL: Invalid argument |
-
-## pal_destroy()
-| **Description** | Destroy the enclave runtime instance |
-| :-: | :- |
-| **Prototype** | int pal_destroy(); |
-| **Parameters** | N/A |
-| **Return value** | 0: Success<br/>-ENOSYS: The function is not supported |
+## 1.pal_init()
+
+### Description
+Initialize enclave runtime with specific attributes.
+
+### Prototype 
+```c
+struct pal_attr_t {
+	const char *args;
+	const char *log_level;
+};
+
+int pal_init(const struct pal_attr_t *attr);
+```
+
+### Parameters
+```
+@args: the enclave runtime specific argument string.
+@log_level: the output log level of enclave runtime.
+```
+
+### Return value
+```
+0: Success
+-ENOENT: Invalid instance path of enclave runtime
+Others: Enclave runtime specific error codes
+```
+
+## 2.pal_exec()
+
+### Description 
+Pass the path of the application to be executed, and synchronously wait for the end of the application to run and return the result.
+
+### Prototype
+```c
+struct pal_stdio_fds {
+	int stdin, stdout, stderr;
+};
+
+int pal_exec(char *path, char *argv[], struct pal_stdio_fds *stdio, int *exit_code);
+```
+
+### Parameters 
+```
+@path: The path of the application to be run.
+@argv: The array of argument strings passed to the application, terminated by a NULL pointer.
+@stdio: The stdio fds consumed by the application.
+@exit_code: Return the exit code of an application.
+```
+
+### Return value
+```
+0: success
+-ENOENT: The path does not exist
+-EACCES: Permission denied
+-ENOEXEC: The path is not an executable file
+-ENOMEM: No Memory
+-EINVAL: Invalid argument
+```
+
+## 3.pal_destroy()
+
+### Description
+Destroy the enclave runtime instance
+
+### Prototype
+```c
+int pal_destroy(); 
+```
+
+### Parameters
+```
+N/A
+```
+
+### Return value 
+```
+0: Success
+-ENOSYS: The function is not supported
+```

rune/libenclave/internal/runtime/pal/spec_v2.md

 # Enclave Runtime PAL API Specification v2
 Enclave Runtime PAL API defines a common interface to interact between `rune` and enclave runtime.
 
-## 1. pal_version
-| **Description** | Indicate PAL API version number implemented by runelet and enclave runtime; runelet is compatible with any enclave runtimes equal to or less than the indicated value. If this symbol is undefined in enclave runtime, version 1 is assuemd by runelet. |
-| :---: | :--- |
-| **Prototype** | `int pal_version();` |
-| **Parameters** | N/A |
-| **Return value** | N/A |
+## 1.pal_version()
+
+### Description
+Indicate PAL API version number implemented by runelet and enclave runtime; runelet is compatible with any enclave runtimes equal to or less than the indicated value. If this symbol is undefined in enclave runtime, version 1 is assuemd by runelet.
+
+### Prototype
+```c
+int pal_version();
+```
+
+### Parameters
+```
+N/A
+```
+
+### Return value
+```
+N/A
+```
 
 ## 2.pal_init()
-| **Description** | Do libos initialization according to the incoming attr parameters. |
-| :---: | :--- |
-| **Prototype** | struct pal_attr_t {<br />    const char *args;<br />    const char *log_level;<br />};<br />int pal_init(struct palattrt *attr); |
-| **Parameters** | @args: Pass the required parameters of libos (can be instance path etc.)<br />@log_level: Log level. |
-| **Return value** | 0: Success<br />-EINVAL: Invalid argument<br />-ENOSYS: The function is not supported |
-
-## 3. pal_create_process
-| **Description** | Create a new process, but do not run it; the real run is triggered by pal_exec(). |
-| :---: | :--- |
-| **Prototype** | struct stdio_fds {<br />    int stdin, stdout, stderr;<br />};<br />struct pal_create_process_args {<br />    char *path;<br />    char *argv[];<br />    char *env[];<br />    struct stdio_fds *stdio;<br />    int *pid;<br />}__attribute__((packed));<br />int pal_create_process(struct pal_create_process_args *args); |
-| **Parameters** | @path: The path of the binary file to be run (relative path in the libos file system).<br />@argv: Binary parameters, ending with a null element.<br />@env: Binary environment variables, ending with a null element.<br />@stdio: The fd of stdio.<br />@pid: If the function return value is 0, pid stores the pid of the new process in libos. |
-| **Return value** | 0: Success<br />-EINVAL: Invalid argument<br />-ENOSYS: The function is not supported |
-
-## 4. pal_exec
-| **Description** | Execute the program corresponding to pid. |
-| :---: | :--- |
-| **Prototype** | struct pal_exec_args {<br />    int pid;<br />    int *exit_value;};<br />}__attribute__((packed));<br />int pal_exec(struct pal_exec_args *attr); |
-| **Parameters** | @pid: The pid of the generation process.<br />@exit_value: The exit value of the process. |
+
+### Description
+Do libos initialization according to the incoming attr parameters.
+
+### Prototype
+```c
+struct pal_attr_t {
+	const char *args;
+	const char *log_level;
+};
+
+int pal_init(struct pal_attr_t *attr);
+```
+
+### Parameters
+```
+@args: Pass the required parameters of libos (can be instance path etc.).
+@log_level: Log level.
+```
+### Return value
+```
+0: Success
+-EINVAL: Invalid argument
+-ENOSYS: The function is not supported
+```
+
+## 3.pal_create_process()
+
+### Description
+Create a new process, but do not run it; the real run is triggered by pal_exec().
+
+### Prototype
+```c
+struct pal_stdio_fds {
+	int stdin, stdout, stderr;
+};
+
+struct pal_create_process_args {
+	char *path;
+	char *argv[];
+	char *env[];
+	struct pal_stdio_fds *stdio;
+	int *pid;
+}__attribute__((packed));
+
+int pal_create_process(struct pal_create_process_args *args);
+```
+
+### Parameters
+```
+@path: The path of the binary file to be run (relative path in the libos file system).
+@argv: Binary parameters, ending with a null element.
+@env: Binary environment variables, ending with a null element.
+@stdio: The fd of stdio.
+@pid: If the function return value is 0, pid stores the pid of the new process in libos.
+```
+
+### Return value
+```
+0: Success
+-EINVAL: Invalid argument
+-ENOSYS: The function is not supported
+```
+
+## 4.pal_exec()
+
+### Description
+Execute the program corresponding to pid.
+
+### Prototype
+```c
+struct pal_exec_args {
+	int pid;
+	int *exit_value;
+}__attribute__((packed));
+
+int pal_exec(struct pal_exec_args *attr);
+```
+
+### Parameters
+```
+@pid: The pid of the generation process.
+@exit_value: The exit value of the process.
+```
 
 ## 5.pal_kill()
-| **Description** | Send signals to processes running in enclave runtime. |
-| :---: | :--- |
-| **Prototype** | int pal_kill(int pid, int sig); |
-| **Parameters** | @pid: Send to all processes if equal to -1, or send to current process if equal to 0, or send to the process that owns the pid if others. <br />@sig: Signal number to be sent |
-| **Return value** | 0: Success<br />-EINVAL: Invalid argument<br />-ENOSYS: The function is not supported |
+
+### Description
+Send signals to processes running in enclave runtime.
+
+### Prototype
+```c
+int pal_kill(int pid, int sig);
+```
+
+### Parameters
+```
+@pid: Send to all processes if equal to -1, or send to current process if equal to 0, or send to the process that owns the pid if others.  
+@sig: Signal number to be sent.
+```
+
+### Return value
+```
+0: Success
+-EINVAL: Invalid argument
+-ENOSYS: The function is not supported
+```
 
 ## 6.pal_destroy()
-| **Description** | Destroy libos instance. |
-| :---: | :--- |
-| **Prototype** | int pal_destroy(); |
-| **Parameters** | NA. |
-| **Return value** | 0: Success<br />-ENOSYS: The function is not supported |
+
+### Description
+Destroy libos instance.
+
+### Prototype
+```c
+int pal_destroy();
+```
+
+### Parameters
+```
+N/A
+```
+
+### Return value
+```
+0: Success
+-ENOSYS: The function is not supported
+```