Merge branch 'ar/config-hooks'

Allow hook commands to be defined (possibly centrally) in the configuration files, and run multiple of them for the same hook event. * ar/config-hooks: hook: add -z option to "git hook list" hook: allow out-of-repo 'git hook' invocations hook: allow event = "" to overwrite previous values hook: allow disabling config hooks hook: include hooks from the config hook: add "git hook list" command hook: run a list of hooks to prepare for multihook support hook: add internal state alloc/free callbacks