Update the manifest to include the new docs

--HG--
branch : distribute
extra : rebase_source : 86f7000b7b66111f5cb39950c3a20575953a4865

MANIFEST.in

 recursive-include setuptools *.py *.txt *.exe
 recursive-include tests *.py *.c *.pyx
+recursive-include docs *.py *.txt Makefile
 include *.py
 include *.txt
 include MANIFEST.in