Bug#861615: ITP: multimc -- A free, open source launcher for Minecraft

[Zebulon McCorkle <zebmccorkle@gmail.com>]

On the following patches:

> * Make the build system install shared libraries to /usr/lib instead 
of /usr/bin (Why does upstream do this? Maybe I'm just installing it
wrong.)
> * Use `~/.multimc` instead of `/usr/bin` as the data directory
(Again, 
why does upstream do this? This one might be a large patch, but I'll 
probably pull request it upstream.)

I'm just going to set /opt/multimc to be the installation prefix, as
that seems to be what the .deb downloadable from multimc.org does.
(though that .deb just installs a script which downloads MMC... guess
that's why I'm doing this)