.arcconfig

encoding: extract stub for fast JSON escape

This moves JSON character maps to pure/charencode.py because they will be
used only when the fast-path fails.

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