Add ignore_localhost config option

[joecorkerton]

Allows users to set the ignore_localhost config option so that exvcr does not record localhost calls. This could be extended in the future to allow users to specify custom domains they wish to ignore.

Use case for this feature - I am trying to write some feature tests with hound. My app calls out to a third party service for some data. I would like to stub this request with VCRs so that my tests pass on CI, but I do not want to stub all of the localhost requests I am making to the headless browser

[coveralls]

Coverage increased (+0.1%) to 93.802% when pulling ed87bdc on joecorkerton:ignore-requests into fdf5988 on parroty:master.

[parroty]

Thanks