Wrapping map producer that performs on the fly meta tiling wrapping another
map producer. It will first peek inside a tile cache to see if the requested
tile has already been computed, if so, it'll encode and return that one,
otherwise it'll build a meta tile, split it, and finally encode just the
requested tile, putting the others in the tile cache.
author: Andrea Aime - TOPP author: Simone Giannecchini - GeoSolutions