Instead of `include_str!()`ing `range_search.rs`, just make it a normal
module under `core::unicode`. This means the same source code doesn't
have to be checked in twice, and it plays nicer with IDEs.
Also rename it to `rt` since it includes functions for searching the
bitsets and case conversion tables as well as the range
represesentation.
Karl Meakin
bf7b05c97b