Wrap in namespace, add YAML support, and only colorize viewport

[S41L0R]

Okay, sorry to bundle three things one PR, but I only thought to do a PR after I had already made all these changes.

1. I wrapped the whole library under a namespace named after it. It was really annoying to have it just be a class with a somewhat generic name. If you want, I guess you can remove this, but I personally think it should be under a namespace.
2. I added basic YAML support.
3. I found that in my 63k line test file colorization performance was very slow. I modified it to only colorize the visible viewport.

[santaclose]

how are you handling multiline comments? I imagine syntax highlighting won't work properly when the beginning of the comment is not visible?