strip tilde and nick from pm message

Personal peeve of mine, as I tend to pm the bot a fair bit. 

I tested manually in pm and in channel.

![screen shot 2014-05-01 at 8 50 36 pm](https://cloud.githubusercontent.com/assets/166648/2858893/ce2a496e-d193-11e3-9bd0-3bde9045b907.png)