New Feature: Protocol support

### New Features:
* Adds protocol support when generating URL helpers, for routes with specific protocol specified.
* Adds support for "protocol relative" base URL value in `:url_links` config.

### Changes:
* `generate_url_link` no longer validates that the `:url_links` config value contains the protocol.

This PR fixes #127.
I'm sorry. I don't understand what you are trying to say. Currently, js-routes does not allow you to use anything but http/https in the `url_links` config value. Otherwise, it will raise an error. My pull request would allow you to use other protocols if you wanted. For example, you could hard-code `ftp://example.com` or specify a protocol relative base URI such as `//example.com` and manually add the protocol like this: `'ftp:' + Routes.my_url`