Include all images from docs in sdist

Include the JPEG images under the docs directory
when creating the sdist.

Resolves issue #20

Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>

MANIFEST.in

@@ -1,5 +1,5 @@
 include setup.py
-recursive-include docs *.rst *.py *.html *.css *.js *.png *.txt
+recursive-include docs *.rst *.py *.html *.css *.js *.png *.txt *.jpg
 recursive-include tests *.py
 include tox.ini
 include LICENSE