Be more lenient about command parsing

I am a cheap bastard and do not intend to pay the exorbitant price of 99¢ for [Tap2Text](https://play.google.com/store/apps/details?id=com.socketsoftware.tap2text). This PR switches command parsing to use regular expressions, which now disregard the text that may follow the command. It also renames `Entry#original_body` to just `body`, and `Entry#formatted_body` to `action`.