Demonstrations for tim2 as capture pwm operation.

1. capture example ：
	FCLK：96M。
	
	timer cycle calculate formula：(period+1)/Freq *(Prescaler)   
								 = (0xFFFF+1)/96000000 * (128)
								 =  0.0873s

2、hall capture config：
	config hall capture ，channel0 capture both edge。
	PB0/PB1/PB2 as hall signal putin PA0/PA4/PA10。