Fixed definition of AGKQuadInsetBottom and new definitions.

Hi,

I've fixed the definition for AGKQuadInsetBottom to update q.bl and q.br instead of q.tl and q.tr.

I've also needed two new functions AGKQuadRotate, AGKQuadRotateAroundPoint that helps rotate AGKQuad better than using AGKQuadApplyCGAffineTransform. It makes use of the function CGPointRotatedAroundPoint that was copied over from the MTGeometry library.

Regards,
Basit