Create bags from command line

[nkrabben]

One of the handy features of the bagit-python CLI is being able to pass it a directory and have it bag the entire thing (a not so handy thing is that it only bags in place). For example,
bagit.py path/to/dir
moves all the contents of path/to/dir to path/to/dir/data and creates the required manifests and info files at path/to/dir

It would be nice to be able to do a similar add with this CLI.