Refactored motor timer. Now using two separated timers: one for event callout, one for timestamping. This allows to reduce interference with motor control logic. In future the timestamping timer IRQ priority will need to be lowered in order to eliminate the interference completely. Also the timestamping function motor_timer_hnsec() was rewritten - now it is completely lock-free (no critical section needed). Some run-time checks were added to main().
Merge branch 'master' of https://github.com/pavel-kirienko/px4esc