Adding maven assembly plugin configuration to create tarballs

Adding maven assembly plugin configuration to create .tar.gz, tar.bz2, and zip tarballs; see issue #316

I'm not sure which of the accessory files if any you would like added (e.g. README.md) so I left that commented out in assembly.xml.

E.g.
https://dl.dropboxusercontent.com/u/87680069/adam-cli-0.13.1-SNAPSHOT-bin.tar.bz2