Added `bin/livereload`

As discussed in #54, I have added an executable script which was previously removed in `2.0.0`. In this PR:

- Added `bin/livereload` to `setup.py's scripts`
- Added `argparse` based script that starts a `livereload` server
    - Defaults port to standard `35729` and watching local directory

Fixes #54

/cc @lepture