Individual cite links

[sneakers-the-rat]

Fix #352

This isn't done, and probably isn't the best way to do this, but figured id open it as a starting point instead of just sitting on it in my fork.

this renders group citations with individual links to each of their cites like this (red border added to accentuate their being separate links)

what it doesn't do is handle styles that would want to render [1-4], but i figured you'd know how to handle that better than i do - i tried to walk up through citeproc to see if i could mimic the process of joining multiple rendered citations, but i couldn't find it. reading ruby is still sort of hard to me, never sure where things get defined.

but if we like this general approach and you have some guidance on how to get that problem resolved, i'll write tests and finish this up