1. Change the type of cmd to 'int';
2. Remove RT_LWIP_USING_RT_MEM macro;

1. Remove RT_LWIP_USING_RT_MEM option;
2. Add waitqueue patch for lwIP 2.0.2;

1. Change 'rt_uint8_t' type of cmd to 'int';
2. Add waitqueue;
3. Split device ipc header files;

1. Add poll/select APIs;
2. Add wait queue implementation;
3. Remove DFS_STATUS_* code and use errno;
4. Add pipe API;
5. Use a standalone fops in DFS;

1. Add POSIX termios implementation;
2. Add POSIX signals implementation;
3. Add stdio for each libc.

Use uint8_t/uint32_t etc to replace u_char/u_long etc;
Use getchar for shell input.