levenshtein: LevenshteinState, usize input distance

[MartinKavik]

Motivation

• Get distance while using Map::search_with_state.

Breaking changes

• Levenshtein::new(query: &str, distance: u32) changed to distance: usize.
• Original automaton state wrapped into LevenshteinState.

Tests

• cargo test --features levenshtein
• New code integrated into the WIP search library I'm working on.