Online documentation needed

[Ivorforce]

See also: #11

NumDot needs some introductions and proper online documentation pages, akin to the godot docs and the xtensor docs.

I cannot say which documentation system is best as i have not worked with any of them myself. It is very possible that the built-in documentation system we'll build in #11 can be used to auto-generate online pages. In that case, that would be the best approach.

[Ivorforce]

Godot updates its online class reference automatically with doxygen, which feeds into Sphinx.

The doc-class primer describes that you have to run make rst in /doc to generate the html files. The Makefile simply runs make_rst.py to generate rst files, which are later adapted in Sphinx.

I proposed this tool get exposed to gdextension. I might take a stab at this myself.

[Ivorforce]

Online documentation is now available: https://numdot.readthedocs.io/en/latest/