updated Doxyfile, turned on warnings

[edwardhartnett]

Fixes #389

Updated the Doxyfile.in to most recent version, also turned on warnings in doxygen to show what remains to be documented.

[fossell]

@edwardhartnett - thanks for demonstrating the warn as error feature. This can be a handy check to ensure new code is well documented by developers. One question, does the workflow abort after the first instance of undocumented routine? Or will it indicate all undocumented routines? Specifically for example in this PRs failed checks, is AVIATION the only file with undocumented subroutine?

[edwardhartnett]

@fossell excellent question. Doxygen can be set to do one of three things:
1 - Print warnings and ignore them (the current settings).
2 - Fail at first warning.
3 - List all warnings and then fail.

After current PRs are merged, we will be in state 1. Doxygen warnings will be in the CI output, but will not cause the build to fail, so CI will still passs.

I have entered another issue (#392) which lists all the current warnings. Once these are fixed, we can turn on checking for new code, which is very worthwhile.

Once we are checking new code, we can fail on first error or fail after all errors.

[fossell]

This make sense and will be a great feature, thanks for the explanation!

[fossell]

@WenMeng-NOAA - This is just an update to the Doxygen file and has no code changes. I approve and it can merged as your discretion.