allow Renderer#render to take a hash of CSL input data

[jrochkind]

Doesn't yet have a spec/features, but needs one. I am having trouble
figuring out where to fit it in to the existing spec structure how, can
you advise @inukshuk on some hints as to what a good spec for this would look like? (I hope not a cucumber features, cause cucumber drives me crazy)

ref #55
ref #53

[jrochkind]

oops, failing travis for real. I'll look into it.

[jrochkind]

Uh, it looks like contrary to docs CiteProc::CitationItem was not the only legal thing to pass into Renderer#render. Something... else was being passed in in tests, which my code turns into a CiteProc::CitationItem and ruins it.

Trying to debug, but appreciate any ideas.

[jrochkind]

it looks like maybe everything is maybe some kind of CiteProc::Attributes, of which CiteProc::CitationItem is one example. Perhaps the doc @param should note that, not sure.

Do note that it looks like Renderer#render is used "under the hood" in things, changes we make there, if they effect performance, may effect other things than top-level manual use of Renderer#render. But I'm not too worried about it.

[krzysiek1507]

Hi! Any chance to merge it?