Regex soft-retweet detection

I added a regex to detect 'RT @' anywhere in the content of a tweet, in
case someone hides a RT in the middle of a tweet! As a bonus, it also
detects a bunch of different types of quotes as well as other things
people might use, like 'via,' 'by,' and 'from'!
Add missing oauth dependency (fixes #40)
Switched to .match for matching

Mispy taught me something about ruby precedence today!
Merge pull request #41 from Stawberri/regex_rt

Regex soft-retweet detection
3.0.3