merge-actions: make merge action a full featured object This open the way for having "smarter" value as action, making the usage code simpler and more flexible. We have to explicitly use __bytes__ call in a couple of place because Python2… Differential Revision: https://phab.mercurial-scm.org/D12114

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