Fix requests stub.  Closes #94
bump version
Add test to demonstrate Python 3 multiple headers bug.
Don't write header values multiple times.

On Python 3, response.msg.keys() contains the same value multiple times if
there are multiple headers with the same value.  Work around this by
converting to a set before iterating over it.
Fix multiple header behaviour.

Join multiple header values together, rather than losing duplicates with a
dict.
Merge pull request #97 from matt-thomson/multiple-headers

Fix serialization/deserialization of multiple headers with the same value
Make defaults of Cassette constructor immutable. Clean up whitespace. Remove unused import.
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.
Revert "Add global toggle to use_cassette."

This reverts commit 366e2b75bbba851325e63499c9770ebcf8f3faf7.

Conflicts:
	tests/unit/test_cassettes.py
Fix failure in test_local_host resulting from attempting to add tuple to list.
use_cassette -> CassetteContextDecorator
Change use_cassette to pass a function to CassetteContextDecorator so that changes to the default settings on the vcr properly propogate.
Failing tests for nested context decoration.