improve github-pages

[ynikitenko]

• center the top button "View On GitHub" vertically,
• create navigation between pages?
• use hacker theme instead of midnight? Decide on its readability first. At the moment fonts are unreadable. Green sections look awesome, but maybe white is less distracting and better for reading a manual?
• can't link to document sections (including manual and inter-manual links),
• can't copy code with a click (as it is done on GitHub); not essential, but nice to have,
• add an arrow "to the top of the page" at the bottom?
• manual still looks a bit better in the terminal.

[ynikitenko]

Some time ago I decided to move to readthedocs completely, because of another (most important) issue: there is no easy way to automatically update github-pages for updated documentation, as is done on readthedocs (and they also store previous versions, which is great).

[ynikitenko]

I moved to readthedocs and Sphinx. There are still some documentation improvements left (like deletion of github-pages - should be done in the next release), but they are no longer related to this issue.