Implement syntax highlight

This is a first attempt to implement syntax highlight, and should solve issue #4.

There're some breaking changes:
* There are no more line numbers
* Text is cropped

Here is why:

As the character count grows, the performance of highlighting the code gets worse. A solution I found was cropping the character count to 3000 chars (may be a little higher). This approach assumes the user won't scroll all the way to the top.

Give it a try and tell me what you think.