ymodem: refactor _rym_read_code

Make fast path fast and slow path slow.
ymodem: increase the default RYM_CHD_INTV_TICK

Frequent 'C' on the handshake will confuse some sender(lrzsz for
example).
Merge pull request #300 from nongxiaoming/master

[bsp] add the linker script file.
Merge pull request #299 from grissiom/next-ymodem

Next ymodem
src/timer: fix a compile warning
Merge pull request #301 from grissiom/fix-timer

[Kernel] src/timer: fix a compile warning
[Drivers] re-write serial framework.
[Build] Fix LPC4300 building.
[Drivers] re-write serial framework.
[bsp] Add BSP for TM4C1294XL (TI Tiva C Series Connected LaunchPad)
Merge pull request #302 from BernardXiong/master

[Drivers] re-write serial framework.
[BSP] remove rt_device_init_all() invoking.
[BSP] remove COMPONENTS_INIT for lpc176x and stm32f107 porting.
[BSP] remove rt_device_init_all() invoking.
[POSIX] fix mq_open and sem_open argument issue.
[bsp] modify the uart_driver to fit the new rt-thread serial device driver framework. Modify the template.uvproj for auto generate MDK project.
Merge pull request #1 from RT-Thread/master

pull rt-thread master
[Docs] Add RT-Thread logo.
[Finsh] fix device_open issue when set_device in finsh.
[bsp] Fix STM32F10x compiling warning.