rust-chg: install logger if $CHGDEBUG is set This is modeled after the example logger and debugmsg() of chg/util.c. https://docs.rs/log/0.4.5/log/#implementing-a-logger

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