Performance optimizations:
1. Triangle rasterization: replaced loops over all the grid cells of the AABB with looping over the area of the triangle itself (i.e. bounds are set per row).
2. Region expansion: instead of sweeping through all the cells at each expandRegion() and finding the right level - sweep once per few levels and divide among several stacks. Left over are appended.
Rasterization optimization: replaced clipping for each individual cell. the clipping line/plane between two adjacent cells is common so data from former cell can be reused if we keep track of the "remaining polygon".
Optimization of of the mesh detail construction: replaced the first of the 2 flood-fill algorithms (the one used to find the span corresponding to the center of the polygon) with a search of span at the center with the region matching the polygon.
Merge branch 'master' of https://github.com/axelrodR/recastnavigation into axelrodR-master