Implementation of secure param for PageUrlAnnotation

There are a few things I am not 100% sure:
- should `$secure` always overwrite the protocol? even if it is not present.
- introduce `$secure` property and getter? Just now I alter the protocol to the current passed value of `$secure`
- comments of the new `$secure` param, quite a lot of information for a single line

Closes #63.
Since normalizer uses given base_url as platform for building final url, then it also will inherit any other parameters from it. This way I can pass some query string in the base url and it will be merged with query string from the `@page-url` annotation. Same for anchor and other parameters.

Maybe we should test all that. It's basically the `merge` method testing.