Clean-up and organize project; resolves #40.

[ruebot]

GitHub issue(s): #40

What does this Pull Request do?

• Moves Docs -> doc
• Moves tests -> src/tests
• Moves headers -> src/headers
• Moves src/*.c -> src/main
• Moves unity -> vendor/unity
• Updates Doxygen config
• Update Doxygen generated docs
• Update README
• Update all src files that need to be updated to reflect re-org
• Update Makefile so project builds
• Clean-up whitespace in src files
• Simplify Makefile

How should this be tested?

It should build, test should pass, and it should still run as it currently does. I've built, and test it with auk locally, and everything appears to be working fine.

Additional Notes:

• I created #49 for the automake support, and the branch for it is here branch is here.

• doxygen version number dropping shouldn't be a problem. It's what was available in apt for Ubuntu 18.04.

[greebie]

Thanks for this Nick. Great clean up job.