Add option to have alternate format when running individual features

[NickClark]

There should be a way to dictate a different format when not running all features. This pull request implements this by adding a new option called failure_format.

When set, running individual features will use this format instead. This is done by inspecting the cli string for a format that does not have an associated --out option and changes the argument.

[netzpirat]

This is a very interesting feature and supports my beliefe that all configuration should go into the :cli option and not into a Cucumber profile.

I find the name failure_format misleading, because it's used for everything except when running all features and thus not only for failures. To stick with the Guard jargon, change_format would be more precise. But a real failure_format, that is used whenever a failed feature is added to the run, would also be a worthy feature :P

I'm very busy over the weekend and I won't have access to a computer until Tuesday, but I'll have a look at this then again.

Thank you very much and have a nice weekend!

[NickClark]

I was struggling over the name as well. I agree that change_format would be better. I'll update it.

Having a true failure_format might be cool, but perhaps not as utilized; unless, that is, someone comes up with a cool new cucumber formatter that, perhaps, weeds out everything except the failing scenarios, instead of showing the entire feature containing the failure.

[NickClark]

Thanks! And I thought you were going to be busy all weekend. :)

[netzpirat]

Just from tomorrow morning until Monday, but not tonight!