string_io: rename to StringIORust to avoid name collusion

rust: add rust dependency without code use

docs: add instruction to run documentation

benchmark: fix json benchmark

benchmarks: update letter benchmark

choice: add more tests for regex pairing and groups

docs: string and char

docs: repeat

docs: map and captures

docs: choice and optioncal

docs: compose and product

docs: use ws_rep0 for better perf

docs: editing

docs: add letter example

docs: temperature, compose example