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/glow_stone.lua

@@ -0,0 +1,25 @@
+-- internationalization boilerplate
+local MP = minetest.get_modpath(minetest.get_current_modname())
+local S, NS = dofile(MP.."/intllib.lua")
+
+local glowstone_def = {
+	_doc_items_longdesc = df_underworld_items.doc.glowstone_desc,
+	_doc_items_usagehelp = df_underworld_items.doc.glowstone_usage,
+	light_source = minetest.LIGHT_MAX,
+	description = S("Lightseam"),
+	tiles = {"dfcaverns_glowstone.png"},
+	is_ground_content = true,
+	groups = {cracky=3},
+	sounds = default.node_sound_glass_defaults(),
+	paramtype = "light",
+	--use_texture_alpha = true,
+	drawtype = "glasslike",
+	drop = "",
+	sunlight_propagates = true,
+}
+if minetest.get_modpath("tnt") then
+	glowstone_def.on_dig = function(pos, node, digger)
+		tnt.boom(pos, {radius=3})
+	end
+end
+minetest.register_node("df_underworld_items:glowstone", glowstone_def)