Add prune.sh example script

This script prunes a map using Minecraft Map Auto Trim.
Read prune whitelists from file

Change `clicraft prune` so that the list of blocks to be kept is
read from a file rather than configured as a giant comma-delimited
list of block ids.
Add blocks.sh example script

Add a script for scraping the minecraft wiki for valid block ids
and printing them in a human-readable format. This format is also
usable as a whitelist for `clicraft prune`.
Install prune.sh using `./configure --with-mmat`