* SpinDelay and SpinDelayUs: now rounding applies instead of truncating
* Document maximum duration of SpinDelay/SpinDelayUs/BUTTON_CLICK/BUTTON_HELD
* Add argument check against max duration in SpinDelay/BUTTON_CLICK/BUTTON_HELD
* Document why these functions don't need to take wrapping into acount as in GetTickCountDelta
* Use >= in the spinning loops
* Clarify StartTickCount calibration operations and use masks AT91C_CKGR_MAINRDY and AT91C_RTTC_RTPRES