Integrate sweave/sphynx

[globusharris]

I've been looking into this and am not convinced Sweave would add any features that aren't already covered with use of roxygen2 and vignettes. Jury's still out on sphinx.

Here are the features I think we ought to have:

1. Help documentation for all functions, including runnable examples
2. Citation generation and reference generation like what's described in the Interpreting Zelig paper (section 3.1).
3. Extensive outward-facing documentation for those who are unfamiliar with differential privacy.

After looking more into how roxygen2 works, it looks like the examples under an @example in the comment blocks are actually run by the package, and thus this is sufficient for the first point. The third is covered by vignettes, which could be extended with sweave if we felt like it but I don't see a clear need. So, point 2 is the only real thing we need to add (right now, citations are just stuck in comments). Looking into ways to do this now.

[globusharris]

For citations (see point 2 above):

• Sphinx has a way to do this, though possibly it only works in the markup files not docstrings so I need to look into that more.
• Zelig uses an actual cite method, which could work, though it mostly works for that project since there's a zelig superclass everything else inherits from, where the cite method is defined. Since we need citations for things that aren't the same type of objects or aren't currently objects at all (e.g. not only mechanisms need citations, but also various utility functions and statistics), this would require significant code restructuring. We could do something similar with a utility function instead of a superclass method, but it wouldn't appear in the docs generated from the roxygen2 docstrings which I don't love.

[globusharris]

Looks like roxygen2 actually also has a reference tag, so we can just use that. The only bummer here is that there's not a good way of, say, generating all of the citations in the package (that I can find).