Added an option to enter your own zoom level. Use -z to set the map at a
particular zoom level. Zoom levels define the width and height in tiles
of the highest zoom level, each new zoom level is twice as wide and
tall. (z=6 -> 2^6 tiles wide and tall)
Implemented tile re-arrangement on map expansion. Now most tiles will
get re-used if your map needs another zoom level! No longer does it need
to re-generate everything.
No longer creates empty directories for tiles, only creates directories
if needed.
Fixed some minor off-by-one logic (and the code that canceled it out to
make it work)
The initial recursive call for tile generation will spawn up to 3 extra
processes to work on each quadrant. It's not perfect yet since some
quadrants may have more or less work to do, and only 4 total workers are
supported.
Also, it waits for all chunks are finished before it dives into the
tiles, to prevent it from using more resources than requested.
