Add doxygen configuration and target to cmake

[alberth]

As requested in #287

Dropped 'dot' to reduce dependencies, and redirected output to the build dir (which unfortunately has to be done with environment variable magic, see http://sourceforge.net/p/doxygen/mailman/doxygen-users/thread/486397E8.4030205@isis-papyrus.com/ )

The output redirection makes that you cannot easily run doxygen outside make, but I guess that's not a problem.

I also had trouble getting the warnings output onto a file, so I dropped the file, and it gets at stderr now.

[xlz]

Warning: Tag `XML_SCHEMA' at line 1797 of file `Doxyfile' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
Warning: Tag `XML_DTD' at line 1803 of file `Doxyfile' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"

I'm using doxygen 1.8.9.1. As is suggested by the warnings, I think it can be removed.

Also, we don't want documentation for internal headers

-EXCLUDE_PATTERNS       =
+EXCLUDE_PATTERNS       = */include/internal/*

With these two changes, the generated html looks good as a basis for more docs.

Also, you might want to note in commit message that the docs are not automatically generated, it needs make doc.

[alberth]

Updated with all suggestions

[floe]

@alberth thanks for your work, merged.

Github pages should be good for hosting the docs, does anybody know if it can auto-run doxygen somehow?

[HenningJ]

Github pages should be good for hosting the docs, does anybody know if it can auto-run doxygen somehow?

Take a look here: http://blog.gockelhut.com/2014/09/automatic-documentation-publishing-with.html