Group cassettes

[hirowatari]

Fixes #700, this will hopefully close that and add the :single_cassette option. See also #761 for a previous pull request.

Some questions I have:

• I think documentation is necessary for this, but was unsure where it should go. I had considered putting it in features/test_frameworks/rspec_metadata.feature.
• I believe that this feature would not apply outside of rspec. Is that correct? I have only used VCR in the context of rspec
• I think unique_cassette might be a better name, but there didn't seem to be any consensus in Add :single_cassette option to RSpec metadata #700, so I just left it.

[hirowatari]

Darn I don't understand why this is failing. Can a maintainer chime in? It works on my local with the same ruby version and same seed so I'm not sure what's up.

[olleolleolle]

  4) VCR::Cassette::HTTPInteractionList has_interaction_matching? does not consume the interactions when they match
     Failure/Error: if VCR.configuration.preserve_exact_body_bytes_for?(self)
       #<Double "VCR::Configuration"> received unexpected message :preserve_exact_body_bytes_for? with (#<struct VCR::Request method=:post, uri=nil, body="", headers={}>)

This was the common test failure. InteractionList tests.

[mcmire]

Not to bikeshed, but just throwing some more ideas for naming out there:

• I feel like use_single_cassette (instead of single_cassette) would be more consistent with the existing configuration values. That said, I don't know if the implication that the requests would be put under a single cassette is obvious enough.
• I'm actually not completely happy with group_cassettes either — does that mean cassettes are grouped in one folder or that the requests that would have shown up in individual cassettes are grouped in one? A better name would be group_requests, although, like use_single_cassette, it's not completely obvious where or how they'd be grouped.
• What about consolidate_cassettes? It's very succinct but I feel like consolidation implies that there is a singular location where everything will be placed, and if you combine multiple cassettes together, cassettes are composed of requests, so by definition you're also combining the requests together too.