More iteration space tiling

Subdividing the iteration space of a loop into blocks or tiles with a fixed maximum size has several advantages. Tiles become a natural candidate as the unit of work for parallel task scheduling. Synchronization between proces-sors can be done between tiles, reducing synchronization frequency (at some loss of potential parallelism). The shape and size of a tile can be optimized to take advan-tage of memory locality for memory hierarchy utilization. Vectorization and register locality naturally fits into the optimization within a tile, while parallelization and cache locality fits into optimization between tiles