Add doc and arglists metadata to defnc macro

[jkxyz]

This PR adds support for an optional doc string parameter to the defnc macro, as well as updating the var metadata with an :arglists key using the props-bindings arg. This is super useful for documenting components and quickly seeing available props in e.g. CIDER's info bar.

---

I understand that this project is not currently being maintained. We're still happy users at Nosco and not planning to move to Helix or another library soon. We've considered forking, but for everyone else using hx, it would be great to get small improvements like this upstream.

[lilactown]

Much appreciated! I know that there are people who use hx out there, so I'm sure they'll appreciate this too :)

[jkxyz]

Awesome, thanks for merging! Do you plan on cutting a new release? I've upgraded our project to include hx as a git dependency.