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 think it is can cause problem, because I can using `itpc` or `ftp(s)` protocols in js links. I can define this flexible by `url_links`, this solution is restrict developers.