docs: build documentation using mkdocs

[DaniBodor]

@JantineSmit, I created a draft pull request for your documentation building branch.
Once you feel it is ready (to be reviewed), you can click "Ready to review" below and tag me (and @psomhorst?) as a reviewer.

closes #233

[psomhorst]

@JantineSmit What is the status of this PR? Is it ready for review? If so, can you click "Ready for review" (above them comment section at the bottom of the page) and mark me as reviewer?

[psomhorst]

I have taken the liberty to:

• rebase the documentation onto the newest version of main
• squash commits
• add a [docs] dependency, removing the mkdocs and all dependencies from [dev]

[psomhorst]

I have updated the docs with:

• split the API into different categories
• streamlining README.md
• only show installation heading on installation page
• formatting of function signatures
• some layout improvements

[psomhorst]

I think this is a great effort that improves the documentation significantly. I have made some changes to make the API page more accessible.

I have already deployed the new documentation to the github.io page. This should from now on be done automatically every time a release is made. There is no way to test this definitively without making a release, so we'll see whether that works the next time we make a release after this PR is merged.

@JantineSmit If you agree with these changes you can go ahead and merge the PR.

[psomhorst]

Great! Deployment of the documentation went as planned, so it should update every time we release a new version.