Use &[char] instead of &str when matching
Use &[char] instead of &str when matching

What this commit does, in substance, is to precompute the code point
boundaries within the choice and query strings, instead of computing
them repeatedly while iterating over the string looking for matches.
This fixes the Unicode handling regressions introduced by 232c718 with
very little performance impact.

rschmitt/heatseeker,rschmitt/heatseeker