.arcconfig

crecord: add `content` properties to all nodes

In order to have a unified API of what can be searched, let's provide
a `content` property to each node type. This way we can search
filenames, context headers (e.g. containing function names, if
deducible from patch context) or changed lines themselves.

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