[MinkowskiSum]clear code, add Triangle and improve GeometryCollection processing
[BreakChange]area2D => area (consistency), complete area implementation
[Length]comments
[MinkowskiSum]comments for the polygon holes
[MinkowskiSum]test insensivity to polygon orientation
improve comments and remove experimental Grid class
Merge pull request #5 from mborne/master

complete area, minkowskiSum