Release v6.9.0 (#182)

* build: prepare v6.9.0-rc1

* build: release v6.9.0

Merge pull request #178 from mammothb/release/v6.8.0

Release v6.8.0

Merge pull request #160 from mammothb/dev

build: prepare 6.7.8 release

docs: update changelog

docs: update version and changelog

refactor: remove unnecessary code in fast distance comparer, update v…

…ersion and changelog

build: update version for release, update documentation for ignore_te…

…rm_with_digits

build: update version for relase