bpo-33297: Mention Pillow to work with more image formats. (#6505)

Also update PIL doc references to Pillow.

Doc/distutils/introduction.rst

@@ -193,8 +193,8 @@ modules using the Distutils:
 module distribution
    a collection of Python modules distributed together as a single downloadable
    resource and meant to be installed *en masse*.  Examples of some well-known
-   module distributions are NumPy, SciPy, PIL (the Python Imaging
-   Library), or mxBase.  (This would be called a *package*, except that term is
+   module distributions are NumPy, SciPy, Pillow,
+   or mxBase.  (This would be called a *package*, except that term is
    already taken in the Python context: a single module distribution may contain
    zero, one, or many Python packages.)
 

Doc/library/tkinter.rst

@@ -800,6 +800,10 @@ reference to the image. When the last Python reference to the image object is
 deleted, the image data is deleted as well, and Tk will display an empty box
 wherever the image was used.
 
+.. seealso::
+
+    The `Pillow <http://python-pillow.org/>`_ package adds support for
+    formats such as BMP, JPEG, TIFF, and WebP, among others.
 
 .. _tkinter-file-handlers:
 

Doc/tutorial/modules.rst

@@ -382,7 +382,7 @@ module names".  For example, the module name :mod:`A.B` designates a submodule
 named ``B`` in a package named ``A``.  Just like the use of modules saves the
 authors of different modules from having to worry about each other's global
 variable names, the use of dotted module names saves the authors of multi-module
-packages like NumPy or the Python Imaging Library from having to worry about
+packages like NumPy or Pillow from having to worry about
 each other's module names.
 
 Suppose you want to design a collection of modules (a "package") for the uniform