add `vendor` folder with `go mod vendor`

add ExecuteStringStd and ExecuteStd for strings.Replacer drop-in repl…

…acement (#23)

Fix possible memory confusion in unsafe slice cast (#21)

* fix possible memory confusion in unsafe slice cast

* update unsafe.go to use simpler, still safe cast

remove vendor as modules supersede it (#15)

Remove dependency on go1.12 from go.mod

v1.0.0 for go with modules (aka go1.11+)