If paginate is a function, call the function to get the url.

[nzhenry]

Else stick with the default behaviour and attempt to resolve the css selector.

Description

Addresses the following issues:

• https://github.com/matthewmueller/x-ray/issues/54
• https://github.com/matthewmueller/x-ray/issues/122
• https://github.com/matthewmueller/x-ray/issues/242

Checklist

• [x] Code compiles correctly
• [x] Created tests which fail without the change (if possible)
• [x] All tests passing
• [x] Extended the README / documentation, if necessary
• [x] Added myself / the copyright holder to the AUTHORS file

[lathropd]

I'm going to close this since it seems pretty specific in the way it's implemented.