Pretty-print the config file. Fix persistence of SMTP port.
Make TLS prompt more clear.
Install notifymail as script in addition to as module.
Remove cron info from README since I can't figure it out.
Add --probe command to check whether mail server is reachable.
Change installed script name to notifymail.py to fix install of module.
Update code snippets in README.
Package for distribution to PyPI.

Specifically:
* Created MANIFEST.in to define the files to distribute.
* Generate README.rst for PyPI in setup.py automatically.
* Remove all raw HTML from README.md because it results in RST containing :raw tags which PyPI disallows.
* Add classifiers to setup.py to improve SEO.