This makes sure that serving the documentation via poetry does not regress
and we have a single way of generating them.
Setting the build backend in `pyproject.toml` makes `pip` to use `poetry` to install the dependencies. By doing so, readthedocs will be able to install the required dependencies to generate the docs (since they don't support poetry directly).
Switches from Sphinx to MkDocs, since it:
* supports Markdown natively without requiring hacks like `eval_rst`
* validates inline links, ensuring that they are not broken
* has a more pleasant live-reloading dev-server
* supports the nicer looking mkdocs-material theme
* is a third of the size of Sphinx (including deps)
The theme change is now possible since Read the Docs have just started
supporting use of custom themes (previously they would override the theme
and use `readthedocs` theme regardless).
Joel Maher
Armen Zambrano
Ed Morley