Remove useless function of spi
Add test nRF
Change some NVIC and control setting
add test_Xbee which is wireless control
Fix input capture bug and enable all remote control

1)Fix the bug in https://github.com/fboris/QuadrotorFlightControl/issues/18
2)Enable all remote control (Roll, Pitch, Yaw, Throttle)
3)Limit the range of remote control signal input(PWM input capture)
Enable the print function (By Xbee now)

Due to the nRF2401 have some programming problem,
we change to use Xbee module through USART.
Enable TIM2 CH3 Interrupt
Merge pull request #19 from zxc2694/master

add test_Xbee which is wireless control
Update README.md
Enable USART_ClearFlag to work USART3
add getch_base() & putch base() to support Serial read/write
Add puts function
Using another method to support printf
Add test_puts
Move the delaytime to the bottom
Add USART_GetFlagStatus before running the USART_SendData.

If no USART_GetFlagStatus, the first character will lose.
Merge to fboris
Fix getch_base() to run correctly
Add gets function
Add test_gets