Feature more descriptive tars

Adding more descriptiveness to the generated archive files per #4 (closed)

This change does a few things:

• --format option has been moved to the inventory stage, so that the inventory will know what the file format is to insert it in to the name. This will hopefully be moot when inventory and suitcase generation are combined
• Added a new option called --prefix. This will allow the user to call the first part of the suitcase whatever they like, but defaults to just suitcase. Happy to change the default, but not sure what it should be
• Added a new option called --user. This will allow for arbitrary username to be entered, but will default to the current running user.

Once run, the actual filenames will be formated as: ${prefix}-${user}-${current-index}-${total-indexes}.${format}