Implement binary search for VPolygon support vector

[mforets]

In #13 we implemented a O(n) algorithm to compute the support vector of a VPolygon. Since the vertices are sorted in CCW fashion by construction, we can do better than that using a binary search, see references below.

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• extreme points in convex polygons in the geomalgorithms site
• Joseph O'Rourke, Computational Geometry in C (2nd Edition), Sect 7.9 "Extreme Point of Convex Polygon" (1998).

[schillic]

Since the vertices are sorted, it should be sufficient to compare a vertex to its neighbors to detect that a maximizing vertex has been found. This optimization scheme is convex, i.e., local extrema are global extrema (however, there can be plateaus).