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_mapitems/crystals_mese.lua

@@ -0,0 +1,59 @@
+-- internationalization boilerplate
+local MP = minetest.get_modpath(minetest.get_current_modname())
+local S, NS = dofile(MP.."/intllib.lua")
+
+--glowing mese crystal blocks
+minetest.register_node("df_mapitems:glow_mese", {
+	description = S("Flawless Mese Block"),
+	_doc_items_longdesc = df_mapitems.doc.glow_mese_desc,
+	_doc_items_usagehelp = df_mapitems.doc.glow_mese_usage,
+	tiles = {"dfcaverns_glow_mese.png"},
+	is_ground_content = true,
+	groups = {cracky=3},
+	sounds = default.node_sound_glass_defaults(),
+	light_source = 13,
+	paramtype = "light",
+	use_texture_alpha = true,
+	drawtype = "glasslike",
+	sunlight_propagates = true,
+})
+
+minetest.register_craft({
+	output = 'df_mapitems:mese_crystal 2',
+	recipe = {
+		{'df_mapitems:glow_mese'},
+	}
+})
+
+minetest.register_node("df_mapitems:mese_crystal", {
+	description = S("Flawless Mese Crystal"),
+	_doc_items_longdesc = df_mapitems.doc.glow_mese_desc,
+	_doc_items_usagehelp = df_mapitems.doc.glow_mese_usage,
+	tiles = {"dfcaverns_glow_mese.png"},
+	groups = {cracky = 2},
+	paramtype = "light",
+	paramtype2 = "facedir",
+	drawtype = "mesh",
+	mesh = "underch_crystal.obj",
+	light_source = 12,
+	is_ground_content = true,
+	sounds = default.node_sound_glass_defaults(),
+	use_texture_alpha = true,
+	sunlight_propagates = true,
+})
+
+minetest.register_craft({
+	output = 'default:mese_crystal 9',
+	recipe = {
+		{'df_mapitems:mese_crystal'},
+	}
+})
+
+if minetest.get_modpath("radiant_damage") and radiant_damage.override_radiant_damage and radiant_damage.config.enable_mese_damage then
+	radiant_damage.override_radiant_damage("mese", {
+		emitted_by = {
+			["df_mapitems:glow_mese"] = radiant_damage.config.mese_damage*12,
+			["df_mapitems:mese_crystal"] = radiant_damage.config.mese_damage*9
+		}
+	})
+end