Class support

[braxtonhall]

I've been thinking about classes in some languages. In Java, changes to a class are almost always the same as changes to a file, so regular git would do the trick. However in other languages, where you can have multiple classes in a file, maybe it would be worth it to trace the changes across files.

This mostly came up because ES5 JavaScript classes are just functions, and the ES6 class keyword is just sheep's clothing.