organize functions in nms4r, supplement with parameter documentation

[superjai]

Hey @bbest - I have gone through and fully documented nms4r as best I could. Considering that the package is well over a thousand lines now, I was having real trouble keeping track of what was what. There certainly is room for improvement, but at least the first pass is done. I documented every single function using the guidance provided here.

As part of going through this whole package, I found several functions that were no longer being used. I deleted all of the unused functions and I was able to prune out quite a bit.

There were a few places in the code I drew a complete blank, where in particular I could use your assistance. There were a few functions I couldn't figure out at all and a few variables I couldn't understand. I flagged those points within spatial.r. On lines where I need your input, I wrote in "BEN". So just do a search for BEN in spatial.R and you'll find all of the places to jump in.

[bbest]

This will also relate to #60 in that we should not only group functions under headers in the References listing of the pkgdown website, but also in different *.R files besides all in spatial.R. So see #60 for ideas on grouping.

[superjai]

Hey @bbest - I have managed to clear up some of the uncertainties, but there are still a few outstanding blanks with your name on it. Do note that there are now four R files in the R folder not just the one spatial.R.

[bbest]

I'm on it with the awesome new Find in Files function in RStudio: