add http verbs options and head label support

[mc706]

Adding label support for the HEAD and OPTIONS HTTP verbs. The RAML spec supports them via their [https://github.com/raml-org/raml-spec/blob/master/versions/raml-10/raml-10.md/#methods](RAML 1.0 Documentation).

This simply adds labels for those methods in the generated HTML so be consistent with the rest of the HTTP verbs