2D polygon interior detection

This function tries to improve the slow Matlab INPOLYGON function.

There are few other fast codes on FEX (e.g., by Darren Engwirda). After exploring many different ways, I come to the conclusion that Darren Engwirda's approach is close to optimal. So here you'll find a general method that share many common aspects, but implemented in C-Mex. I have makes few contributions: (1) a lean C-implementation, (2) Using Matlab SORT and HISTC for binning, (3) Derive an empirical rule when to apply the sorting, (4) a more rigorous on-boundary detection.