Refactored random map generator system and added several terrain generators.

Created a global list to track base turfs for explosions/shuttle moves.
Remaps the asteroid to be a moonlet. Tidies up some references to 'asteroid', removes moonbase from the accessible z level list.

code/modules/random_map/_random_map_setup.dm

@@ -0,0 +1,22 @@
+/*
+	This module is used to generate the debris fields/distribution maps/procedural stations.
+*/
+
+#define MIN_SURFACE_COUNT 500
+#define MIN_RARE_COUNT 200
+#define MIN_DEEP_COUNT 100
+#define RESOURCE_HIGH_MAX 4
+#define RESOURCE_HIGH_MIN 2
+#define RESOURCE_MID_MAX 3
+#define RESOURCE_MID_MIN 1
+#define RESOURCE_LOW_MAX 1
+#define RESOURCE_LOW_MIN 0
+
+#define FLOOR_CHAR 0
+#define WALL_CHAR 1
+#define DOOR_CHAR 2
+#define EMPTY_CHAR 3
+#define ROOM_TEMP_CHAR 4
+#define MONSTER_CHAR 5
+#define ARTIFACT_TURF_CHAR 6
+#define ARTIFACT_CHAR 7