[REF] implement internals as dir

pandas/core/internals/__init__.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# flake8: noqa
+from .blocks import (
+    Block,
+    ObjectBlock,
+    DatetimeTZBlock, DatetimeBlock, TimeDeltaBlock,
+    CategoricalBlock, ExtensionBlock,
+    SparseBlock,
+    FloatBlock, IntBlock,
+    NonConsolidatableMixIn,  # used by test_external_block
+    make_block,              # generic, io.packers, io.pytables, test_internals
+    _block2d_to_blocknd, _factor_indexer, _block_shape,  # io.pytables
+    _safe_reshape)           # io.packers
+
+from .managers import (
+    BlockManager, SingleBlockManager,
+    items_overlap_with_suffix,         # reshape.merge
+    create_block_manager_from_arrays,  # core.panel, core.frame, sparse.frame
+    create_block_manager_from_blocks)  # core.frame, core.panel
+from .concat import concatenate_block_managers