Adding compact subcommand

[sjoblomj]

Many operations, like remove, can leave gaps in the archives. This PR adds the compact subcommand to rebuild the archive which shrinks its size.

[sjoblomj]

I was thinking of adding a --compact flag to the add and remove subcommands as well, which seems convenient to me, but I'm not sure...

Especially add already have plenty of arguments. And if the user tries to --compact with archives that don't have internal listfiles, the command would fail (unless we allowed providing listfiles in those subcommands as well - but that adds further complexity and cognitive load on the user when trying to understand how to use the tool). I'm leaning towards letting the user manually run mpqcli compact afterwards instead of providing convenience flags to add and remove. What do you think?

[thomaslaurenson]

Nice addition - looks good to merge as is. I will delete the 0.9.10 release I made yesterday and make it into a new 0.10.0 release, as there were so many changes that it deserves a minor version bump, not just patch. Will include this PR in the release.