Merge pull request #100 from IvanMalison/immutable_keyword_defaults

Make defaults of Cassette constructor immutable. Clean up whitespace. Re...
Clean up __init__.py .
Merge pull request #101 from IvanMalison/minor_cleanup

Clean up __init__.py .
Add use_cassette class so functinos that are decorated with use_cassette can be called multiple times.
Bump version number for new use_cassette_decorator.
Add global toggle to use_cassette.
Add before_record_response to Cassette and VCR.
Change default paramters to VCR from lists to tuples.