3.12.0

CHANGES:

• Add \u{hex-escape} syntax (@anmonteiro,
  #2738)
• Support local open and let bindings (@SanderSpies) #2716
• outcome printer: change the printing of @bs.* to @mel.* (@anmonteiro, #2755)
• Fix outcome printing of optional arguments on OCaml 5.2 (@anmonteiro, #2753)
• support parsing and printing of external%extension (@anmonteiro, #2750, #2766, #2767)
• install refmt manpage (@anmonteiro, #2760)
• add support for parsing / printing of refutation clause in switch (@anmonteiro, #2765)
• support let%ppx in signatures (@anmonteiro, #2770)