Data out-of-date -- docs/all-error-codes.md

[gsjaardema]

Not sure if it matters, but discovered while grepping the code tree for an error code translation that the values in all-error-codes.md are incomplete and in some cases incorrect. For example NC_EBADGRPID is -116 in netcdf.h, but listed as -113 in all-error-codes.md

[DennisHeimbigner]

I wonder if we could build a tool using e.g. awk to automatically
create all-error-codes.md from netcdf.h?

[edhartnett]

The error codes are actually poorly documented in netcdf.h.

I suggest that we fix up the error documentation there.

I don' t think that programmers will naturally look to a separate documentation file for information, so I think all-error-codes.md is perhaps not needed.

[DennisHeimbigner]

A perhaps simple solution is to provide the documentation in the
doxygen documentation for the nc_strerror function and
modify all-error-codes.md to just tell people to look at the documentation for
nc_strerror. That way, at least everything is in a single file.

[edwardhartnett]

I believe we should remove all-error-codes.md, and in nc_strerror() we should simply refer to netcdf.h.

In netcdf.h we should (as we already have) document each error code with a doxygen comment.

If we do all this, doxygen will display the error codes just fine:

I will submit a PR with this change.

(Furthermore, when referring to these constants in the doxygen, we need to preceed them with a double-colon. Like ::NC_EACCESS

If we do that then the error code will be hyper-linked to it's definition in netcdf.h.)