Use reversed to iterate through list backwards (#374)

As using slicing syntax on `list`s makes a copy, use `reversed` instead
to avoid the copy and just create a generator for iterating through the
`list` backwards.

Author: jakirkham

zarr/core.py

@@ -1735,7 +1735,7 @@ def _decode_chunk(self, cdata):
 
         # apply filters
         if self._filters:
-            for f in self._filters[::-1]:
+            for f in reversed(self._filters):
                 chunk = f.decode(chunk)
 
         # view as numpy array with correct dtype