Add support vector for VPolygon

[mforets]

given a set of 2d vertices, the support vector of a VPolygon <:LazySet can be computed by:

• sorting vertices by polar angle (see function <=)
• performing binary search for the given direction

a convex hull preprocessing maybe needed, in general.

in a similar manner to HPolygonOpt, there can be a VPolygonOpt for warm-starting.

[mforets]

a convex hull preprocessing maybe needed, in general.

we perform the convex hull on the construction of each VPolygon, by default.

we plan to do a straightfoward implementation first and leave the binary search approach for later (see this geomalgorithms entry).

[mforets]

done in PR #41