Use cl-the annotations as a source of types

[ebpa]

I don't see anything in the project yet that mentions the cl-the macro. I think it would a great source of type information.

[Fuco1]

Seems interesting! I actually had a similar idea adding elsa-cast or something to add type info to forms. The downside is that elsa would then become a run-time dependency of the package.

We can add some cl-the but it is probably pretty limited in what it can express.