Allow to configure allowed levels by string value (#22)

* feat: allow to configure level from string

* fix staticcheck violation

* fix UTs

* fix: apply suggested changes

* fix: apply some of the suggested changes

* fix: more idiomatic code

* Update level/level.go

Co-authored-by: Márk Sági-Kazár <sagikazarmark@users.noreply.github.com>

Co-authored-by: Márk Sági-Kazár <sagikazarmark@users.noreply.github.com>

Simplify stack helpers and remove internal/stack package (#11)

README: remove disclaimer

Initial import from go-kit/kit (#1)

* Initial import, minus logrus and zap

* GitHub Actions for CI

* gofmt

* Satisfy staticcheck

* It was a nice idea

* Satisfy staticcheck