Need a way to include header values in generation of fixture filenames

[aneilbaboo]

I have a situation where requests differ by different header values. Specifically, To be specific, I'm hitting Google's API.ai service and have tests which depend on hitting different apps I've created on that service, where each app is only identified by the bearer token. Obviously, this is messing up my tests.

Can I get sepia to generate fixture filenames using header values?

[aneilbaboo]

PR #23 solves this issue.