Don't bother linking to Parameter.__init__; just linking directly to Parameter will do since that's where its __init__ parameters are documented.
Making sharedmethod subclass classmethod seems like an all around good
idea--from a class's point of view, and from the point of view of any
code inspecting a class's __dict__ (particularly, API doc generation
by sphinx) this makes a sharedmethod indistinguishable from a normal
classmethod which is as it should be.