added msPerFrame() for performance profiling
added msPerFrame() for performance profiling

added 21 x 13 rows (tile-screen), one extra row and column to
allow for room to shift tile-screen one tile in any direction.
For when player is running in whatever direction engine only
has to draw edge tiles.

mwharris1313/webgl-poc,mwharris333/webgl-poc,mwharris333/webgl-poc,mwharris1313/webgl-poc