Add jpt

[glyn]

This would be particularly useful because it implements RFC 9535.

https://rubygems.org/gems/jpt (not yet published on github)

KittyMac/Sextant#10 (comment)

/cc @cabo

[cabo]

Gem source is now at https://github.com/cabo/jpt
(I worked on this on our university gitlab.)
Haven't done README, LICENSE etc., as I didn't need this during PoC development

[cburgmer]

Alright, I've figured out how to call it, just now need to understand whether we can separate internal processing errors from selector parse errors (aka "unsupported").