remove the unneeded cache layer. the cache is for writing. we're just
reading. all the cache is doing is adding latency as it makes its copies
of map data structures.
generating a 190x190x100 dig blueprint:
before change: 1.7s
after change: 1.0s
the performance gains aren't as important here as the reduced complexity
of the algorithm, though. for reasonably-sized blueprints, the time
savings are unnoticeable.
//Translates a region of tiles specified by the cursor and arguments/prompts into a series of blueprint files suitable for digfort/buildingplan/quickfort