Upping the ante from D2015 / D2016, this diff is a proof of concept of what it
takes to annotate an actual module, making types visible for all functions /
methods. I'm using as guinea pig swh-graph, as it is largely independent from
the rest and only requires swh-{core,model} which are already (minimally)
typed.
To avoid duplication of typing information, I'm removing here types from
docstring and moving them to proper type annotations. I'm not exactly sure yet
what Sphinx rendering (with Napoleon style) will do with type annotations...