If someone is using flake8 and piping it to a command like `head`, the
command they are piping flake8's output too may close the pipe earlier
than flake8 expects. To avoid extraneous exception output being printed,
we now catch IOErrors and check their errnos to ensure they're something
we know we can ignore.

This also provides flexibility to add further errnos for ignoring on a
case-by-case basis.

Closes #69

This got lost in Vancouver somewhere

This is a quickfix to help openstack unbreak their gate requirements

https://gitlab.com/pycqa/flake8/issues/40

* Adding an ignore option in [flake8] wasn't working because pep8.StyleGuide
turned the string sent in into a tuple, which the option parser needs to receive
as an iterable that isn't a string. Split on spaces, commas, or semicolons using
re.findall in order to get a list of error/warnings to pass to StyleGuide
properly.

* Add self to contributors

(cherry picked from commit 8f8a7d458f8f46669398591bffd93462d4e439ed)

When ignore is an empty string, it will apparently not run any checks at
all. Using None as the default ensures that it does run the appropriate
checks.

Closes #52