Added multiple see links

Hi guys,

I was missing a functionalities for adding multiple "see" references and customizing the "see" link text. I created a commit, that allows it. 

Here are the examples of multiple "see" links added to one method description:
see "v2#general#index_include", :desc => "including additional fields"
see "v2#general#index_query"
def index
end

I also kept the backward compatibility, so all the existing code should work the same way.

Probably it's also worth to update the documentation if you like my changes.

Best regards,
Kamil