pass flake8 + related tox configuration

flake8 is a style utility which wrap pep8/flake8 and mccabe if availabe.
I have added a tox environnement to easily run it.

The E501 (line too long) error is ignored, it does not play well with
the inlined examples in comment blocks.

To run:

 tox -eflake8
Merge pull request #52 from hashar/pep8-pyflakes

pass flake8 + related tox configuration
Bump to 0.8.5.
Add ExactSequence for tuple-like positional matching.
Exclusive Marker
Remove unexpected non-ascii trash.
Fixes for Python 2.6
Merge pull request #68 from vartagg/master

Exclusive Marker
add waffle.io badge
Merge pull request #69 from waffle-iron/master

waffle.io Badge
Move waffle badge.
Allow for subclasses of Invalid to be raised by validators.
Merge pull request #71 from uber/mk_invalid_subclassable

Allow for subclasses of Invalid to be raised by validators.
Inclusive marker
Merge pull request #74 from xsleonard/inclusive

Inclusive marker
Document how to use Url().

Fixes #76.
Optional keys can have defaults.  Adds unittest to Optional

Fixes #47.
Added specific errors for most validation errors
Increased test coverage by a tiny bit...
Changed comments to docstrings