[MinkowskiSum,OffsetPolygon]ignore empty geometries
[MinkowskiSum,Offset]test empty cases
Merge branch 'master' of https://github.com/Oslandia/SFCGAL
[StraightSkeleton]Polygon and MultiPolygon
[Extrude]Solid and MultiSolid in switch case
licence in headers
[StraightSkeleton]test num geometries
Merge pull request #8 from mborne/master

licence & straight skeleton