Add methods for multi-polygons.
Test multi-polygon init, fix a multi-polygon init bug.
Test insert, remove polygons.
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Terraformer.xcodeproj/project.pbxproj
Merge pull request #19 from mbcharbonneau/master

Mutli-polygon methods + tests