Add VCR-like functionality

[petRUShka]

There is great Ruby tool VCR(https://github.com/vcr/vcr) that provide caching requests instead of mocking.

Record your test suite's HTTP interactions and replay them during future test runs for fast, deterministic, accurate tests.

It would be great to have such functionality in PhantomXHR.

[jamescryer]

I agree, this would be a great feature. Record and 'export' of both XHR and user events would be incredibly useful. Would really love to see a PR for this

[sulabhjain]

+1