RFE: Add Doxygen Github Pages

[drakenclimber]

This patchset automatically generates Doxygen documentation and writes it to a github branch. Github supports a feature called pages where a branch is displayed as HTML, and I'm using that to then render the Doxygen output.

Here's what it looks like on my personal libseccomp repo: https://drakenclimber.github.io/libseccomp/index.html

A couple more comments:

• I'm only generating Doxygen for the main branch. If we wanted to generate Doxygen for the release branches as well, we could publish each branch to a subfolder. Then we could make a simple index page
• I added a simple introduction to seccomp.h.in so that the start page isn't empty. Definitely room for improvement here

[drakenclimber]

This could close issue #195

[coveralls]

Coverage remained the same at 89.601% when pulling f2548f2fb21d8e2274c372eb48deb6a6f9f134d8 on drakenclimber:issues/doxygen into 51b50f95e1fb717e4560818f8b90b7ebde314ad1 on seccomp:main.

[drakenclimber]

Really just that one question regarding hiding the API macro, but I'm good with this either way. I'll refrain from merging this due to that question, but if there is no good answer go ahead and merge it @drakenclimber.

I would really prefer to resolve the question over the API stuff before we merge it. The only thing worse than missing documentation is wrong/misleading documentation :)

[pcmoore]

I would really prefer to resolve the question over the API stuff before we merge it. The only thing worse than missing documentation is wrong/misleading documentation :)

Fair enough :)

FWIW, I found these suggestions while quickly googling the issue:

• https://www.doxygen.nl/manual/faq.html#faq_code
• https://www.doxygen.nl/manual/commands.html#cmdcond

[pcmoore]

In an effort to get v2.6.0 out sooner than later, I'm going to suggest we push this out to v2.7.0; if you have any concerns or objections please drop a comment.