Use DeviceDriver ringbuffer.
Add hardware flow support.
Use new struct serial_ringbuffer.
Fix uart device driver for gpio remap and hardware flow control.
Add uart4 and uart5 device driver.
Merge pull request #241 from bright-pan/master

Add RTS/CTS option in the serial framework.
Fix rt_serial_control() bug for customized command and indent the code
Merge pull request #242 from bright-pan/master

Fix rt_serial_control() bug for customized command and indent the code
Revert "Merge pull request #241 from bright-pan/master"

This reverts commit 5aeedc4f3a3c3fcfffb0cd4a474f5faa75053839, reversing
changes made to 3d80e414ff6c03ff04fecb914e7aa9b3fb535e03.

This merge breaks every uart driver in all BSPs. @bright-pan , is there
any way to get this done without breaking existing code?
Merge pull request #243 from grissiom/serial-rollback

Revert "Merge pull request #241 from bright-pan/master"
1.replace API prefix usb* with usbh* in USB host stack to distinct with USB device stack;
2.adjust some viable and micro name
3.some other small fix
Merge branch 'master' of https://github.com/RT-Thread/rt-thread
[DeviceDrivers] Add watchdog driver frame work
[DFS] fix compiling warning for NFS file system
[DFS] fix compiling warning in NFS
[Kernel] stop thread timer when suspend a thread
[Kernel] declare more APIs in module
[Finsh] Use msh as prompt when current mode is msh mode.
[Pthreads] fix compiling warning
Add more command to msh for module.
[Finsh] fix the shell prompt issue.
modify the pixel format to RGB565 in sdl_fb.c