Rewrite orchard.xref

[alexander-yakushev]

Big redoing of orchard.xref that includes:

• Improved performance.
• Getting rid of eval (yikes).
• Cleanup and compaction.

---

• You've updated the changelog (if adding/changing user-visible functionality)

[bbatsov]

Thanks for looking into this! How did you even think of revisiting it?

I was wondering if the past if this is useful in its current state or no (and even considered replacing it with some xref that just uses regular expressions like swank-clojure did), but I guess it's better to have it than not to have it, and we're going to have it - it's better to optimize it. :-)

[alexander-yakushev]

Just was cruising through the repo and found a namespace I haven't touched before:).

I'm not sure if anybody ever uses it, but now at least it's in a state that is not embarrassing to keep:).