private void updateThumbPosition() {
		int thumbAngle = (int) (mStartAngle + mProgressSweep + mRotation + 90);
		mThumbXPos = (int) (mArcRadius * Math.cos(Math.toRadians(thumbAngle)));
		mThumbYPos = (int) (mArcRadius * Math.sin(Math.toRadians(thumbAngle)));
	}
Notification that the user has finished a touch gesture. Clients may
want to use this to re-enable advancing the seekarc.

@param seekArc
           The SeekArc in which the touch gesture began
SeekArc_library/src/com/triggertrap/seekarc/SeekArc.java