Completely change biome code again

Turns out my previous grasp of how Minecraft does this was wrong.

This seems to be the correct way. One side effect is that biome data
now has less resolution. One only really notices this when looking at
water, for which Minecraft does not even use the water colours for
in-game, otherwise I can't really tell a big difference.

Fixes #1698.

overviewer_core/biome.py

@@ -14,31 +14,17 @@
 #    You should have received a copy of the GNU General Public License along
 #    with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
 
-import numpy
 
-class BiomeDispensary:
-    """Turns biome arrays of either 256 or 1024 integer values into 16x16 2d arrays,
-    which can then be retrieved for any Y level with get_biome.
-    """
-    def __init__(self, biome_array):
-        self.biome_len = len(biome_array)
-        if self.biome_len == 256:
-            self.biomes = [biome_array.reshape((16, 16))]
-        elif self.biome_len == 1024:
-            self.biomes = [None] * 16
-            # Each value in the biome array actually stands for 4 blocks, so we take the
-            # Kronecker product of it to "scale" it into its full size of 4096 entries
-            krond = numpy.kron(biome_array, numpy.ones((4)))
-            for i in range(0, 16):
-                # Now we can divide it into 16x16 slices
-                self.biomes[i] = krond[i * 256:(i + 1) * 256].reshape((16, 16))
-
-
-    def get_biome(self, y_level):
-        if self.biome_len == 256 or y_level < 0:
-            return self.biomes[0]
-        else:
-            # We clamp the value to a max of 15 here because apparently Y=16
-            # also exists, and while I don't know what biome level Mojang uses for
-            # that, the highest one is probably a good bet.
-            return self.biomes[min(y_level, 15)]
+def reshape_biome_data(biome_array):
+    biome_len = len(biome_array)
+    if biome_len == 256:
+        return biome_array.reshape((16, 16))
+    elif biome_len == 1024:
+        # Ok here's the big brain explanation:
+        # Minecraft's new biomes have a resolution of 4x4x4 blocks.
+        # This means for a 16x256x16 chunk column we get 64 times for the vertical,
+        # and 4x4 values for the horizontals.
+        # Minecraft Wiki says some dumb thing about how "oh it's ordered by Z, then X, then Y",
+        # but they appear to either be wrong or have explained it with the eloquence of a
+        # caveman.
+        return biome_array.reshape((4, 64, 4))