Merge pull request #241 from bright-pan/master

Add RTS/CTS option in the serial framework.
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. Add hardware flow support.
2. Fix the serial buffer size from fixed-sized to user-defined.
3. Use new ringbuffer data structure.
Port uart driver for new serial driver framework