Clarify failed initial state in tokenizer tests.
Infer block argument types.
Spec is fixed; smarmy comments obsolete.
Consume and emit character tokens with multiple characters.
Don't bother copying childNodes on every access.

It's awful for performance. The array only mutates within the parser, so a
couple well-placed -copy calls obviate the need to constantly copy.
Unique and freeze character sets used when parsing selectors.

They get called a lot during parsing, so making many of them is slow. And
immutable character sets are faster than mutable ones.
Version bump.