fix tox envlist
Add Exception when JSON Serializing Binary Data

Since I can't think of a good way to deal with this, let's just give a
nice error message to point people in the right direction.

Closes #51
remove failing test since I'm not going to fix this use case
pep8
clean up readme whitespace
Add Logging

This helps to figure out which matcher has decided your two cassettes
differ, and figure out when your cassettes have hit the network.

Closes #34
Filter Sensitive Data From Requests

Add the ability to filter out sensitive data, using one of three
methods: from headers, from a query string, and by using a custom
callback to modify the request.

Closes #67
Add waffle badge