Deletes the mcra server tool. We have no more use for it.
mcmapgen supersedes it.
Applies another major refactoring.

Implements mcconv tool. It converts a Minecraft world to a custom binary
file format (MCB) which is more efficient for our purposes. It omits a lot of
data we have no need for and employs a file layout which is more suitable
for fast processing of all map data. Whereas standard Minecraft data is
organized for easy, sparse probing of chunks. We have no use for that.

In tests, mcconv can reduce a world of ~10Mb in size, down to about
380Kb. Apart from skipping all entity data, it achieves this by
also omitting all Bedrock and Air blocks. These too serve no purpose
in our applications and consequently saves us a great deal of space.
Lastly, we do not compress individual chunks. All chunks and blocks
are written to a region file as-is and then the entire file is
GZIP compressed.

Any other tools in this repository will hence forth require an MCB-
formatted world as input.