Jupyternotify

Added
- Added the ability to load the magic in a notebook via `%load_ext jupyternotify` (from beckermr)

Added
- Added feature where clicking on the notification body changes focus to the window and tab with the notebook (from Darel13712)

Added
- Added line magic %notify to trigger notifications mid-cell (from bensteers)
- Added %autonotify line magic to automatically notify after a certain length of time threshold (from bensteers)
- Added --output/-o option to use cell output as message (from bensteers)
- Added a jupyter notebook to run through the tests specified in the README

Added
- Added some badges to the README and PyPI

Fixed
- Fixed a small formatting typo in the README

Added
- Added the ability to customize the displayed message