NIW API

I actually reread NIW.R and figured out what I was doing that night (I did write it at night, all night; it was terrible and great). It's now usable. 

The HEAD commit says [BROKEN] but the parts you care about are not: you can read the code to check what's what and source("NIW.R") to play with it. It's `test.correctness.main.R` that's broken. Pushing because I hope to catch you still awake ;)