.arcconfig

templatekw: add compatlist() as a replacement for showlist()

Just like compatdict(), this is mostly a copy of showlist(). showchildren()
is ported to the new API as an example.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}