Enable syntax highlighting for Rakefile and other similarly named files

Hi,

When I noticed I wasn't getting any highlighting in my Rakefile it was slightly confusing, I spent a lot of time trying to enable colors, eventually discovering that it was the Rakefile that was not supported.

So this is a small commit to enable syntax highlighting in Rakefiles and a few others.

There are no specs, as I couldn't find any existing ones around the ```CodeFile``` class. However, I can add a few if required.

Cheers,