Instead of relying on magic comments, explicitly encode the source.

Guys,

I am using Sinatra with IronRuby and we have found an issue related to how IronRuby handle encodings:

https://gist.github.com/1849043

That said, I have modified tilt to explicitly encode the source, similarly to Rails, instead of relying on magic comments.

Definitely this is rather a IronRuby bug but Tilt already works around JRuby and 1.9.1 bugs, I thought I would try getting this in to ensure compatibility across all implementations.

PS: If you guys agree, please don't merge this just yet. I am doing more evaluations, the point of this pull request is just to get some early feedback. <3