Add support for complimentary channel output and deadtime.

This patch enables output on the complimentary channels (TIMx_CHyN).
For timers 1 and 8, deadtime can also be inserted when the channels
transition. For the pyboard, TIM8_CH1/CH1N and TIM8_CH2/CH2N can
take advantage of this.
Merge pull request #900 from dhylands/comp-deadtime

Add support for complimentary channel output and deadtime.