Generalize the 'data run' idea
Use byte scans for attribute value states
Don't use the webapp spec as a tokenizer benchmark

It takes forever.
Intern the tokenizer's "last start tag name"

Saves an allocation and copy much of the time.
Use foster parenting for non-space table text
Change the tree builder interface around appending stuff
Implement foster parenting
Fix travis link.

[kmcallister: fixes #4]
Move NodeEnum into its own file
RcDom fixes
Remove useless `#[macro_escape]`s

This should be a module attribute, and anyway isn't needed because these macros
are used down the module hierarchy but not up.