Use "capability" rather than "handle"

[tomjaguarpaw]

Until now I've been talking about "handles" but it seems there is some precedent for calling them "capabilities", for example Martin Odersky's Keynote at ICFP '24. Perhaps we should switch.

[lxsameer]

+1 to this. "handler" is confusing

[tomjaguarpaw]

There was a small typo: the thing suggested to rename is "handle" rather than "handler" ("handlers" also exist, and I can't think of a better name).