feat(*): create keyword functions
* chore(*): update messages and gherkin, relocate Keyword
* chore(*): update messages and gherkin, relocate Keyword
* chore(*): update messages and gherkin, relocate Keyword
* feat(*): mandate keyword type when unambiguous keyword function is used
* test(*): keyword type in feature files
* docs(*): update step-by-step walkthrough to mention the option of using keyword functions
* docs(*): update CHANGELOG.md
* test(*): keyword substeps
* chore(*): go mod
