As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
Instead of using string everywhere, have the CSS parser produce enum
values, since they are a lot nicer to work with.
In the future we should generate most of this code based on a list of
supported CSS properties.
