Merge pull request #25 from jessieay/master

Index action should join resource keys
Renames SurrogateControlHeaders to SurrogateKeyHeaders
* better represents what this helper *actually* does
* updates comments to reflect actual
Don't do a service get before purging
* adds purge_by_key method to FastlyRails::Client
* updates ActiveRecord and Mongoid purge methods
* tests
Reduce the coverage of stub_request
* In reality it's only used to stub api.fastly.com/login
* add stub_request for purge URL
bump to v0.1.5
Update CHANGELOG [skip ci]
Merge pull request #27 from fastly/no-service-get-in-purge

Purge without fetching the service first
Merge pull request #26 from fastly/rename-to-surrogate-key-headers

Rename SurrogateControlHeaders to SurrogateKeyHeaders