Eliminate most std:: imports
Build with #![no_std]
Ditch std::ascii

When it moves into core and/or collections, we can drop some of this code.

See rust-lang/rust#16801.
Switch from HashMap to TreeMap for tokenizer profiling

Because HashMap requires libstd and a task-local RNG (by default).
Allow building the library without libstd at all
Implement a C API for the tokenizer