create docs section Internal Modules

docs/PIL.rst

@@ -123,12 +123,3 @@ can be found here.
     :members:
     :undoc-members:
     :show-inheritance:
-
-:mod:`_binary` Module
----------------------
-
-.. automodule:: PIL._binary
-    :members:
-    :undoc-members:
-    :show-inheritance:
-

docs/reference/internal_design.rst

@@ -7,4 +7,4 @@ Internal Reference Docs
   open_files
   limits
   block_allocator
-
+  internal_modules

docs/reference/internal_modules.rst

@@ -0,0 +1,38 @@
+Internal Modules
+================
+
+:mod:`_binary` Module
+---------------------
+
+.. automodule:: PIL._binary
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
+:mod:`_tkinter_finder` Module
+-----------------------------
+
+.. automodule:: PIL._tkinter_finder
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
+:mod:`_util` Module
+-------------------
+
+.. automodule:: PIL._util
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
+:mod:`_version` Module
+----------------------
+
+.. module:: PIL._version
+
+.. data:: __version__
+    :annotation:
+    :type: str
+
+    This is the master version number for Pillow,
+    all other uses reference this module.