Fixed GetMapEdge rounding errors, added grid helpers

Using floor on floats was causing off-by-one errors on the magnitude of
entire tiles, and the player would occasionally pop out in the wrong
place. Now GetMapEdge uses integers to represent rows and columns and
only converts them to float positions at the end of the calculation.
Removed commented-out code
Merge branch 'master' of https://github.com/mdechatech/radplatformer