Use Cargo-ified rust-phf

Until we Cargo-ify html5ever, it's necessary to manually build rust-phf before running make.
Rust upgrade misc
Make the tokenizer macros hygienic
Convert the tree builder's unexpected!() macro to a function

Avoids hygiene issues.
Work around rust-lang/rust#16617
Update for rust-phf changes
Remove some unnecessary mut
Rework use of lookahead_and_consume! to avoid mut borrows in pattern guards
More Rust upgrade misc
Pass -C rpath
Work around rust-lang/rust#16643
Eliminate "use super::*" in mod test
Change Show for Atom so to_string() is consistent with as_slice()
Rust upgrade misc for tests
Add Cargo.toml.
Add Huon to AUTHORS
Tweak Cargo.toml
Use Cargo to build the library