Rename project to "odd" (odoc docs)
Rename the package, binary, and library from odoc-switchdocs/switchdocs to
odd: opam package `odd`, command `odd <subcommand>`, library module `Odd`.
Knock-on renames: the stale marker is now `.odd-stale`, state lives in
var/cache/odd, the SWITCHDOCS_DRIVER env var becomes ODD_DRIVER, the zsh
completion is _odd, and the opam hooks and docs refer to `odd`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>