Initial codebase

I'm committing this as a work in progress. If anyone has any suggestions or feedback, it's welcome!

TODO:

[ ] Render image as base64
[ ] Gather extra data (subject, domain from)
[ ] Output JSON with some extra data and the base64 image
[ ] Create config loader for base path, destination url etc.
[ ] Make sure Gmail forwarding formatting is removed properly
[ ] See what formatting other clients add (Mail.app, etc.)
[ ] Make sure the app is deployable on Heroku