Proposed fix for encoding issue

Possible fix for <a href="https://github.com/robfletcher/betamax/issues/135">Issue #135</a>.

The issue was that binary response bodies were being saved in encoded form, and played back after being encoded once more in BetamaxFilters. The fix was to save compressed response bodies in human readable form on tape and encode on their way to the browser.
Are you using the proxy server? From the current state of the code, I'd expect the httpclient approach to work with gzip.

A better short-term fix for gzip would be to remove the gzip/deflate logic (2 lines without test coverage) from BetamaxFilters.java.