river 0.3.2

This release updates the required Zig version to 0.12.

It also switches from using git submodules for dependency management to using
the Zig package manager. Distro packagers should read the new Zig package
manager section in PACKAGING.md for tips on how to handle this change.

Full changelog:

Isaac Freund (6):
      build: bump version to 0.3.2-dev
      build: update to Zig 0.12
      build: add -Dno-llvm build option
      build: switch to the Zig package manager
      ci: drop FreeBSD CI for now
      build: bump version to 0.3.2