Option which enables generation HTML with assets served over HTTPS

If you would like to host generated documentation over HTTPS it is impossible to do it properly, because of assets that are fetched from CDN only via HTTP. 

`raml2html` module supports this as an option - I've prepared PR with support for `https` option in the compiler, and I've also fixed the failing tests (something is wrong with matching by whole content - I've switched it over to seeking specific text in the generated output).

Please let me know if these changes are appropriate for you and if the version bump is okay as well (`0.1.8`).