pip install --upgrade flake8  # http://flake8.pycqa.org
python2 -m flake8 . --exclude=third_party --ignore=E1,E306 --max-line-length=80

* move functools.py to stdlib
* move md5.py to stdlib
*  move re.py re_tests.py sre_*.py to stdlib

Fixes: https://github.com/google/grumpy/issues/123

* Remove dependence on pip.
* Add osx to Travis test matrix.
* Remove pip upgrade and sudo requirement for Travis config.

* added groupby, izip_longest, permutations, product, combinations and combinations_with_replacement.
* added corresponding tests.
* make chain to be a iterator
Signed-off-by: Cholerae Hu <choleraehyq@gmail.com>

I sense that you folks are making progress on `re`, etc.  The next line points readers to the wiki list that should be more complete and easier to keep up to date.