Squashed commit of the following:

commit 9b646e2
Author: Tom Augspurger <[email protected]>
Date:   Tue Sep 11 14:07:15 2018 -0500

    Doc fixup

commit b1aac08
Author: Tom Augspurger <[email protected]>
Date:   Tue Sep 11 13:57:18 2018 -0500

    API: register_extension_dtype class decorator

    Closes pandas-dev#22664

Author: TomAugspurger

pandas/core/dtypes/base.py

@@ -127,7 +127,8 @@ class ExtensionDtype(_DtypeOpsMixin):
     * _is_numeric
 
     Optionally one can override construct_array_type for construction
-    with the name of this dtype via the Registry
+    with the name of this dtype via the Registry. See
+    :meth:`pandas.api.extensions.register_extension_dtype`.
 
     * construct_array_type
 
@@ -138,6 +139,11 @@ class ExtensionDtype(_DtypeOpsMixin):
     Methods and properties required by the interface raise
     ``pandas.errors.AbstractMethodError`` and no ``register`` method is
     provided for registering virtual subclasses.
+
+    See Also
+    --------
+    pandas.api.extensions.register_extension_dtype
+    pandas.api.extensions.ExtensionArray
     """
 
     def __str__(self):

pandas/core/dtypes/dtypes.py

@@ -11,6 +11,8 @@
 def register_extension_dtype(cls):
     """Class decorator to register an ExtensionType with pandas.
 
+    .. versionadded:: 0.24.0
+
     This enables operations like ``.astype(name)`` for the name
     of the ExtensionDtype.
 

pandas/tests/extension/json/test_json.py

@@ -118,6 +118,7 @@ def assert_frame_equal(self, left, right, *args, **kwargs):
 class TestDtype(BaseJSON, base.BaseDtypeTests):
     pass
 
+
 class TestInterface(BaseJSON, base.BaseInterfaceTests):
     def test_custom_asserts(self):
         # This would always trigger the KeyError from trying to put

pandas/tests/extension/test_integer.py

@@ -20,7 +20,7 @@
 from pandas.tests.extension import base
 from pandas.core.dtypes.common import is_extension_array_dtype
 
-from pandas.core.arrays import IntegerArray, integer_array
+from pandas.core.arrays import integer_array
 from pandas.core.arrays.integer import (
     Int8Dtype, Int16Dtype, Int32Dtype, Int64Dtype,
     UInt8Dtype, UInt16Dtype, UInt32Dtype, UInt64Dtype)