also don't keep adjusted maps around if not necessary

(instead, `walint --version` will now just say "unknown")

as annoying as yaml is, cabal's package format is somehow worse, apparently

If --version is given, `walint` prints version information, then exists
with code 0.

(and no one's documented that)

Anyways it now uses utf8 which seems a little more reasonable.

Among them
 - always set correct exit codes
 - refuse to write out files if the out path already exists
 - calculate the overall severity correctly
 - slightly changed the json output schema
 - also output the text output format in json
 - make the default config.json suitable for a production environment

(didn't do anything, and it seems better to do all of these things in
the config anyways)