Tokenize numeric character references
Upgrade to Servo's new Rust version
Move extract-from-spec.py

And fix the header.
Partial support for named character references
Move some ASCII functions into util
Move Rust code into src/

Also fix module visibility and add .gitignore.
Handle failure to extend a previous char ref match

e.g.:

    &not    => match for U+00AC
    &noti   => valid prefix for &notin
    &notit  => can't continue match

Here we need to reconsume "it" and not just the most recent character.
Correctly flag an error for char refs in 0x80..0x9F
Upgrade rust-phf for deterministic builds