Add ability to scale sheer walls.

Pummel on the face of a wall you can't dig with your bare hands
and eventually you will find handholds there, allowing you to
climb.

This will hopefully provide an immersive alternative to /stuck
for getting out of pits, which will also make players have to
carefully extricate themselves from their situations instead of
just using /stuck to bail and then running home to come back
with supplies.

mods/nc_scaling/depends.txt

@@ -0,0 +1,2 @@
+nc_api
+nc_api_craft

mods/nc_scaling/init.lua

@@ -0,0 +1,78 @@
+local modname = minetest.get_current_modname()
+
+local maxdist = 4
+
+minetest.register_node(modname .. ":steps", {
+	paramtype = "light",
+	paramtype2 = "facedir",
+	sunlight_propagates = true,
+	tiles = {
+		"nc_scaling_blank.png",
+		"nc_scaling_blank.png",
+		"nc_scaling_blank.png",
+		"nc_scaling_blank.png",
+		"nc_scaling_blank.png",
+		"nc_scaling_steps.png"
+	},
+	use_texture_alpha = true,
+	drawtype = "nodebox",
+	node_box = nodecore.fixedbox(-0.5, -0.5, 31/64, 0.5, 0.5, 0.5),
+	walkable = false,
+	climbable = true,
+	pointable = false,
+	buildable_to = true
+})
+
+nodecore.register_limited_abm({
+	label = "Scaling Decay",
+	interval = 1,
+	chance = 1,
+	limited_max = 100,
+	nodenames = {modname .. ":steps"},
+	action = function(pos)
+		local n = minetest.get_meta(pos):get_string("n")
+		if n then
+			local pl = minetest.get_player_by_name(n)
+			if pl and vector.distance(pl:get_pos(), pos) <= maxdist
+			then return end
+		end
+		minetest.remove_node(pos)
+	end
+})
+
+nodecore.register_craft({
+	label = "compress coal block",
+	action = "pummel",
+	duration = 5,
+	normal = {x = 1},
+	check = function(pos, data)
+		if vector.distance(data.crafter:get_pos(), pos) > maxdist then return end
+		if not data.wield:is_empty() then return end
+		local node = minetest.get_node(pos)
+		local def = minetest.registered_nodes[node.name]
+		return not nodecore.toolspeed(data.wield, def.groups)
+	end,
+	nodes = {
+		{
+			match = {walkable = true}
+		},
+		{
+			x = 1,
+			match = "air",
+			replace = modname .. ":steps"
+		}
+	},
+	after = function(pos, data)
+		local p = data.rel(1, 0, 0)
+		local d = vector.subtract(p, pos)
+		local fd = 0
+		for i = 0, #nodecore.facedirs do
+			if vector.equals(nodecore.facedirs[i].f, d) then
+				fd = i
+				break
+			end
+		end
+		minetest.set_node(p, {name = modname .. ":steps", param2 = fd})
+		minetest.get_meta(p):set_string("n", data.pname)
+	end
+})