Refactor tempo api, include quarter-note distance in frames method.

Refactor tempo api, include quarter-note distance in frames method.

	- moves frame rounding up to TempoMap, which is needed
	  in order to calculate pulse distance without frame rounding.

	- the time unit for tempo is still minute, but this now also
	  applies to meter sections. (new audio locked meter sections no
	  longer require a frame position).

	- there is no longer a discontinuity
	  in the pulse for audio-locked meter/tempi.

	- temporarily add debugging output in Region::set_position()
	  to test for region beat not matching region frame.