Semicolon escape sequence ";;" in evolutions. [#585, #1543, #212] 

As per [the discussion thread on play-framework-dev](https://groups.google.com/forum/#!topic/play-framework-dev/hHOSqoh8nUU), this allows users to escape semicolons in their Evolutions by using double semicolons: `;;`

Still waiting on some feedback before updating docs...