More randomness for slime chunks

The old code caused a diagonal pattern. If some x,z was a slime chunk, then so was x+1,z-1.
Use a classic pseudo-random hashing approach instead, by multiplication of chunk numbers
with large primes that should be more random.
Also make slime density and light level configurable.

Allow using a 3d chunking system where y is also used.

@@ -9,0 +13,4 @@
+local slime_max_light = (tonumber(minetest.settings:get_bool("mcl_mobs_slime_max_light", true)) or minetest.LIGHT_MAX) + 1
+-- maximum light level for swamp spawning
+local swamp_light_max = 7
+-- maximum highzt to spawn in slime chunks

@@ -9,0 +8,4 @@
+-- slime density, where default N=10 is every 10th chunk
+local slime_density = math.floor(tonumber(minetest.settings:get("mcl_mobs_slime_density")) or 10)
+-- use 3D chunking instead of 2d chunks
+local slime_3d_chunks = minetest.settings:get("mcl_mobs_slime_3d_chunks") or false

@@ -9,0 +10,4 @@
+-- use 3D chunking instead of 2d chunks
+local slime_3d_chunks = minetest.settings:get("mcl_mobs_slime_3d_chunks") or false
+-- maximum light level, for slimes in caves only, not magma/swamps
+local slime_max_light = (tonumber(minetest.settings:get_bool("mcl_mobs_slime_max_light", true)) or minetest.LIGHT_MAX) + 1

@@ -88,2 +27,2 @@
-assert(calculate_chunk_value(vector.new(16,0,64)) == (3), "calculate_chunk_value failed")
-assert(calculate_chunk_value(vector.new(-160,0,-160)) == 0, "calculate_chunk_value failed")
+local math_floor = math.floor
+local math_max = math.max

@@ -224,0 +224,4 @@
+# Slime chunk density
+mcl_mobs_slime_density (Slime chunk density, default is one in ten, 0 to disable cave slime) int 10 0
+# Use 3d chunking instead of 2d chunking
+mcl_mobs_slime_3d_chunks (Use 3d chunking instead of 2d chunking) bool false