Check PEP-8 as part of continuous integration

Fixes #80. Changes mostly per @eriknw. At the moment, no errors are
ignored. We may wish to add exceptions as agreed upon down the road.
Add PEP-8 exception to ignore Sphynx's conf.py
Add pypy exception for PEP-8 checks.

pypy barfs badly when doing PEP-8 checks. PEP-8 should be
platform-independent anyways. This commit prevents the pep8 check on
pypy.
Merge branch 'master' of github.com:pytoolz/toolz into travis-pep8
PEP-8 fix on test_memoize.py
Show all PEP-8 warnings (including repeats)
PEP-8 tweak of test_memoize_kwargs.py
Merge pull request #82 from eigenhombre/travis-pep8

Check PEP-8 as part of continuous integration