describe-package: Better type representation

[josephjclark]

Adaptor docs doesn't currently show any type information on parameters (or return types, which may be less useful).

We need to a) extend describe-package to include good, human-readable descriptions of types, and b) render those types in adaptor-docs.

This gets particularly interesting with complex types, like objects.

I've started to add type analysis to describe-package but this issue is a reminder to take it further.