Useful documentation

[noah1510]

One of the most important things is missing at the moment and that is some at least half decent documentation.

Here are a few suggestions on what should be done, feel free to propose additions in the comments:

• [x] adding a doxyfile to build html documentation (#69)
• [x] build and publish the documentation to github pages or something different (github actions or maybe travis)
• [ ] document all functions (javadoc style)
• [ ] document every type, enum and class (javadoc style)
• [ ] properly document the examples
• [ ] write some kind of getting started/beginners guide

[h4tr3d]

I recreate gh-pages branch, make it with clean history.