Add MEDRectCenterInRect
Merge pull request #20 from github/center-rect

MEDRectCenterInRect
Merge branch 'master' into align-rect

Conflicts:
	Archimedes/CGGeometry+MEDConvenienceAdditions.h
	Archimedes/CGGeometry+MEDConvenienceAdditions.m
	ArchimedesTests/MEDCGGeometryAdditionsSpec.m