This is mostly to get the grunt work of the way. This is split up into
multiple commits to hopefully make it more manageable to review.
Note that these are not full implementations, and the bindings mostly
get the low hanging fruit.
Also implements some attributes that I kept out because they had
dashes in them. Therefore, this closes#2905.
Instead of creating extremely common FlyStrings like "id" and "class"
on demand every time they are needed, we now have AttributeNames.h,
which provides Web::HTML::AttributeNames::{id,class_}
This avoids a bunch of string allocations during selector matching.
