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_underworld_items/config.lua

@@ -0,0 +1,27 @@
+local CONFIG_FILE_PREFIX = "dfcaverns_"
+
+df_underworld_items.config = {}
+
+local print_settingtypes = false
+
+local function setting(stype, name, default, description)
+	local value
+	if stype == "bool" then
+		value = minetest.setting_getbool(CONFIG_FILE_PREFIX..name)
+	elseif stype == "string" then
+		value = minetest.setting_get(CONFIG_FILE_PREFIX..name)
+	elseif stype == "int" or stype == "float" then
+		value = tonumber(minetest.setting_get(CONFIG_FILE_PREFIX..name))
+	end
+	if value == nil then
+		value = default
+	end
+	df_underworld_items.config[name] = value
+	
+	if print_settingtypes then
+		minetest.debug(CONFIG_FILE_PREFIX..name.." ("..description..") "..stype.." "..tostring(default))
+	end	
+end
+
+setting("bool", "invulnerable_slade", true, "Slade is invulnerable to players")
+setting("bool", "destructive_pit_plasma", true, "Pit plasma destroys adjacent nodes")