fix docs after codecs merge

Author: alimanfoo

docs/api.rst

@@ -8,6 +8,5 @@ API reference
     api/core
     api/hierarchy
     api/storage
-    api/compressors
-    api/filters
+    api/codecs
     api/sync

docs/api/codecs.rst

@@ -0,0 +1,20 @@
+Compressors and filters (``zarr.codecs``)
+=========================================
+.. module:: zarr.codecs
+
+This module contains compressor and filter classes for use with Zarr.
+
+Other codecs can be registered dynamically with Zarr. All that is required
+is to implement a class that provides the same interface as the classes listed
+below, and then to add the class to the ``codec_registry``. See the source
+code of this module for details.
+
+.. autoclass:: BloscCompressor
+.. autoclass:: ZlibCompressor
+.. autoclass:: BZ2Compressor
+.. autoclass:: LZMACompressor
+.. autoclass:: DeltaFilter
+.. autoclass:: FixedScaleOffsetFilter
+.. autoclass:: QuantizeFilter
+.. autoclass:: PackBitsFilter
+.. autoclass:: CategorizeFilter