log: pack filematcher and hunksfilter into changesetdiffer object
This is just a way of getting rid of clumsy makefilematcher/makehunksfilter
arguments. There might be a better abstraction, but I don't think this is bad.
This makes filematcher and hunksfilter available by default, but that should
be fine.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}