[#75691732] Document vcloud-core public methods

> According to semver http://semver.org/ we should document the API
> (lower case should). We should document this by adding Yard
> documentation to public methods. See [#73962736] for an example.
You can mark optional parameters with an optional keyword [doc](http://www.rubydoc.info/gems/yard/file/docs/Tags.md)