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.
unix: Add comment about needed dependencies for MICROPY_FORCE_32BIT.
unix: Update comment MICROPY_GCREGS_SETJMP (untested -> undertested).
Merge pull request #900 from dhylands/comp-deadtime

Add support for complimentary channel output and deadtime.
README: Update "unix" section with more info/details.
Merge branch 'modure' of https://github.com/pfalcon/micropython into pfalcon-modure
stmhal: Enable ure module (tests pass on pyboard).
Merge branch 'pfalcon-modure'
Merge pull request #902 from pfalcon/readme-unix

README: Update "unix" section with more info/details.