Polymorphic Relations are not supported

[RahulDey12]

Synopsis:

Polymorphic Relations are not supported

Proposed Syntax:

morphTo: attendable
morphMany: Attendance

Expected Behavior:

That should add a Polymorphic relation

[jasonmccreary]

I like it. Should be a pretty easy addition if you'd like to try opening a PR for it. No worries if it doesn't have tests, I can add them afterwards.

Otherwise, I'll open this up to the community...