Add ==, !=, +, - operators to NSPoint/NSRect/NSSize
Add Top/Left/Right/Bottom helpers for NSRect for better compatibility with RectangleF
Use CGFloat/NSRect/NSPoint/NSSize instead of float/RectangleF/PointF/SizeF for better cross compatibility
Add conversion operators to/from NSRect/Point/Size and System.Drawing.RectangleF/PointF/SizeF