using the new falling node hooks provided by `bg_api`, add alternative
versions of existing stoneworking recipes, where instead of pummeling, a
stoney node must fall onto the input nodes with sufficient force.
note that since the only currently existing stoney node that can fall,
loose cobblestone, is unobtainable without cheats, so are these recipes.
pummeling definition tables now has lists of item id:s and groups, the
same way e.g. ABM:s do, that determine what items are involved in a
recipe.
update existing (in-use) pummel recipes to make use of this.
rename mods; add `bg_` prefix.
add hacky cleanup ABM (couldn't get LBM:s to work), that converts old
nodes into new ones according to this rename.
the cleanup doesn't do anything for items, though.