Change include directory in Makefile. Add peripheral codes.
Add stm32f4xx_conf.h.
Exclude file system temporalily.
Add stm32f4xx libraries.
Change CPUCLOCK.
Fix a bug that would break context switch.
Set up USART1.
Put rom file system back.
Add gdb macro to see the current task.
Remove some debug code. Set current_task to global variable.
Fix a bug which make SysTick_Config fail.
Disable nested-interrupt in interrupt.