Rename the `e` function to `dancepill`

People may have other commands aliased to `e` already. This keeps the original
usage intact (source dancepill/e; e package.tar.gz) while allowing people to
re-alias `e` to something else and keep a hold of the original dancepill
function.

Example of the usage this commit allows:

    # inside ~/.bashrc or whatever
    source path/to/dancepill/e
    alias extract=dancepill
    alias e='emacsclient -t'