Improve documentation

[asgersvenning]

Currently the documentation page is not super easy to navigate and the following things need to be implemented:

1) A collapse-able menu on the left-hand side, where you can see the currently selected page and its' nesting in the content hierarchy.
2) Cross-links to referenced functions throughout the documentation.
3) Links to source code both on the documentation page, but also the Github source.
4) A proper front page.
5) Examples/tutorials.

It would also be great to remove the intermediate index.html and perhaps also (although at a lower priority) think about mobile accessibility.

[asgersvenning]

It would also be great with an installation and testing guide, as well as system requirements.