Remove toolbox directory, sync with source from GSW-Python

[efiring]

This includes and supercedes #20. The additional changes are:

• It makes the .c and .h files from GSW-C exactly match those in GSW-Python.
• The .c files can now be compiled as c++ so that the code can be built with MSVC.
• The toolbox directory is eliminated, greatly simplifying the process of maintaining the code and keeping it in sync with the version in GSW-Python.

In fact, it might be easier to make changes and test them via Python and then copy them over to GSW-C than to go in the opposite direction.

[dankelley]

@efiring Thanks for the skype call yesterday. I did a success build with the new C code, along with a bunch of tests. I wrote up notes in markdown but GH won't let me attach them, so I'm attaching a variant of the notes in PDF. The summary is that there is virtually no chance of harming GSW-R users by incorporating the new C code. It's been half a year since I updated GSW-R, and I'm inclined to plan an update whenever you feel that GSW-C is OK (and GSW-Python is OK). As mentioned on the skype call, there is a resistance to updating R packages, so I'd prefer to wait until things are settled in C and Python land, before making a new release that affects only a single function.

Speaking of that function, it would be great if I could get some python-based check values for gsw_geo_strf_dyn_height_1, because that is a rare function in GSW-R, in lacking test values in its docs.

Thanks again.

gsw.pdf

[ocefpaf]

I wrote up notes in markdown but GH won't let me attach them, so I'm attaching a variant of the notes in PDF.

I'd love to see a wiki, where Markdown is OK, with those notes but the PDF is fine. Thanks for the transparency.

[dankelley]

@ocefpaf I hope it's ok with the others, but I set up a wiki for this repo, and https://github.com/TEOS-10/GSW-C/wiki/2018-06-01-test-efiring-simplify-branch-in-GSW-R now holds the notes on my test. Thanks.

[ocefpaf]

Thanks! We have many R and Python users in our group that are quite interested in having these two packages consistency. This is very helpful.