Use autodoc to generate the documentation

[james-d-mitchell]

In Semigroups v4.0.0, we started using autodoc to produce the documentation, this has a number of advantages, and can be used with the current documentation sources (i.e. doesn't require to re-write the manual completely). I was prompted to make this issue by @mtorpey's comment on #549, about where to add author's names, if we convert to using autodoc, then we will only have to put the author's in a single place.

[github-actions[bot]]

Stale issue message