Update the hatter/bin script.

Now uses /usr/bin/env ruby to launch hatter.
Add contributing.md.
Fix bug preventing the running of commands.
Add more stuff to the config file.

- Our email address for sending mail
- The delivery method used when sending mail.
- Key to compose mail.
Refactor command_factory and add exception handling.
Implement the ComposeCommand.
Merge pull request #14 from expez/send-mail

Makes it possible to use Hatter to send mail.