* The main thread priority can be configured by Kconfig;
* Add the checking of kernel object type, which can effectively avoid the problem of continuing to use kernel objects after they are destroyed.
* Add the idle hook list to mount multiple idle hook, and can be configured by Kconfig.
* Add the device_ops operation set to reduce the footprint of device object.
* Remove the special memory operation in application module when using SLAB memory management algorithm.
* Move application module from the kernel to `libc/libdl`.
* Enhance the debug information output of `rtdbg.h` file.
* In Keil/IAR tool chain, the `RT_USED` is used to keep symbols and avoid to add more argument or section in link phrase.
## Components
* Remove all of external codes, which will be moved to packages in the future.
* Add initialization flag for shell, file system, network protocol stack etc to prevent repeated initialization;
* Enable the long file name feature of ELM FatFs in default.
* Change DFS FD to dynamic allocation mode. The maximum number of allocation is still DFS_FD_MAX.
* Add dfs_fdtable_get() function to get different fdtable;
* Add more DFS error messages, and provide easy to understand log when abnormal.
* Fix the disk format issue of FatFs file system when multiple FatFs file systems are mounted.
* Remove the folder enter feature in msh when input a folder name;
* Add `int finsh_set_prompt (const char * prompt);` routine for setting a custom prompt for msh;
* Add the VBUS configuration in Kconfig.
* Move the application module from kernel to `libc/libdl` component;
* Rewrite most of the management code for application module: replace the original object container with the object list; split the symbol resolution code into different processor architecture etc.
* Update the application module chapter in the programming guide, and change it into dynamic module chapter.
* Overwrite the exit() function of newlib to take over the processing of exit for a dlmodule.
* Add SAL (Socket Abstraction Layer) component for adapting different protocol stacks and network implementations, and update the relevant sections of the programming guide;
* Add AT component, including AT client, AT server and AT Socket function;
* Remove the poll/select API of DFS_NET and move them to SAL component.
* Remove the strong dependence of lwIP component for DFS_NET and replace it with Kconfig configuration in SAL.
* Add the DHCP server function with lwIP raw API;
* Fix the wait queue none-initialization issue in socket allocation of lwIP.
* When a thread is about to block on a wait queue, fix the wake up issue for `rt_wqueue_wakeup' is executed to wake up that thread;
* Add the PWM driver framework;
* Fix the sdio_irq_wakeup release issue in the MMC/SD framework.
* Fix the problem of DMA handling in the serial driver framework.
* Update SFUD to v1.0.6 version;
## BSP
* Fix the SP issue when hard fault occurs for ARM Cortex-M arch;
* Add C-Sky CK802 architecture porting;
* Add Realtek amebaz WiFi SOC (rtl8710bn) BSP;
* Update imxrt1052-evk firmware SDK to support B model chip.
* Fix the copying packets issue in the Godson 1C BSP when sending message.
* The Nuvoton m05x/m451 BSP are changed into the main() entry mode, and supports GCC compilation;
* Fix the inconsistency issue between touch range and LCD resolution in qemu-vexpress-a9.
