Tiles generator for HDR environment maps

Splits an HDR env map into tiles/bins that roughly have the same radiance.

Red: generated bins - Blue: random samples using importance sampling by the tiles

These generated tiles can be used for importance sampling the environment map in a Monte Carlo Ray Tracer. Each tile has is a 4-tuple of (x0, y0, x1, y1) which marks the absolute min and max values of a tile's area.