Modpack refactor (#4)

Split this mod into a set of sub-mods in a modpack, and in the process did a whole bunch of renovations.

* updated Subterrane's API to allow for more patterned placement of things
* added "warrens"
* clean separation of flooded and non-flooded caverns
* rearranged biomes to make cavern layers more distinct
* added oil layer
* added underworld layer

df_trees/init.lua

@@ -0,0 +1,66 @@
+df_trees = {}
+
+--grab a shorthand for the filepath of the mod
+local modpath = minetest.get_modpath(minetest.get_current_modname())
+
+--load companion lua files
+dofile(modpath.."/config.lua")
+dofile(modpath.."/doc.lua")
+dofile(modpath.."/aliases.lua")
+
+local S, NS = dofile(modpath.."/intllib.lua")
+
+df_trees.register_all_stairs = function(name, override_def)
+	local mod = "df_trees"
+
+	local node_def = minetest.registered_nodes[mod..":"..name]
+	override_def = override_def or {}
+	
+	-- Note that a circular table reference will result in a crash, TODO: guard against that.
+	-- Unlikely to be needed, though - it'd take a lot of work for users to get into this bit of trouble.
+	local function deep_copy(table_in)
+		local table_out = {}
+	
+		for index, value in pairs(table_in) do
+			if type(value) == "table" then
+				table_out[index] = deep_copy(value)
+			else
+				table_out[index] = value
+			end
+		end
+		return table_out
+	end
+	
+	local node_copy = deep_copy(node_def)
+	for index, value in pairs(override_def) do
+		node_copy[index] = value
+	end
+		
+	if minetest.get_modpath("stairs") then
+		stairs.register_stair_and_slab(
+			name,
+			mod ..":" .. name,
+			node_copy.groups,
+			node_copy.tiles,
+			S("@1 Stair", node_copy.description),
+			S("@1 Slab", node_copy.description),
+			node_copy.sounds
+		)
+	end
+	if minetest.get_modpath("moreblocks") then
+		stairsplus:register_all(mod, name, mod..":"..name, node_copy)
+	end
+end
+
+dofile(modpath.."/blood_thorn.lua")
+dofile(modpath.."/fungiwood.lua")
+dofile(modpath.."/tunnel_tube.lua")
+dofile(modpath.."/spore_tree.lua")
+dofile(modpath.."/black_cap.lua")
+dofile(modpath.."/nether_cap.lua")
+dofile(modpath.."/goblin_cap.lua")
+dofile(modpath.."/tower_cap.lua")
+
+dofile(modpath.."/torchspine.lua")
+
+