better documentation required for the _text attribute calls, in C and Fortran

[edhartnett]

As kindly pointed out by @gsjaardema in #1510, the documentation for the nc_get/put_att_text is confusing. There needs to be a longer discussion of the following:

• In C, a text string is an array of char, terminated by a NULL.
• Does the length include the NULL (this is a user choice)
• What does the API mean by calling these _text?
• How does this relate to the NetCDF-4 model String type?

Also, this should be clarified not just in the C but also in the Fortran docs.

I think netcdf does a fine job on documentation, but it must be acknowledged that we are programmers and we tend to write as little documentation as we can get away with - sometimes less. This is not a case of just changing a sentence or two, but adding a few paragraphs of explanation.

[edhartnett]

OK, there is even more to do here. When I build the latest master, and build the docs, and navigate to the documentation for nc_get_att_text(), it is wrong! It is the documentation for nc_get_att(). So that needs to be fixed as well.

[edhartnett]

OK, even more fun. ;-) The current way the documentation is done is not actually correct. What is done is that all the atomic type functions are grouped together, and described by one documentation block. But this causes the function name links to not work properly. So you can go to the Attributes section, and see all the functions properly, but if you click on nc_get_att_int() in the documentation, the function docs cannot be found. I am trying to find a good way to fix this without just duplicating the documentation everywhere.