Allow (key, newvalue) pairs in filter_query_params() and filter_headers() so keys can be redacted rather than removed.
Add debug logging to ReplayRecordingManager
Rewrite ReplayConnectionHelper for urlretrieve()

Not all users of httplib will call ReplayConnectionHelper.retrieve(),
instead some of them (such as urllib.urlretrieve) call the underlying
sequence directly.  This rewrite allows httreplay to support a wider range
of calling libs.
Save text responses as quoted-printable so they're readable (and editable) in the recordings.
Add ReplaySettings.allow_network (default True for compatibility).