Added width & height members to Tile, moved local functions to utility.*pp

I've added more members to the Tile structure, namely the width & height
of the tile. This is to fix a circular logic problem, which is too
abstract for this commit message ;)

I've also moved the local/static/inline/etc. utility functions to their
own module in the common directory, because this is just cleaner that
redefining the same code a dozen times.

The map's logic is still the same, but I need to keep moving; I've been
procrastinating far too much.