Allow trailing / in link href.

[JulienPalard]

fixes #285

[geemus]

I'm concerned about removing this much of the validation. I hate working with regexes, but maybe we should try to modify it to allow this rather than just dropping it? What do you think?

Also, this change looks like it broke the tests, so we'll want to fix them (and probably expand them to ensure we continue to support the trailing slash for you).

Thanks!