Additions to Request and Response

* Add Request specs
* Add Response specs
* Alias is_*? predicates to *?
* Add 307 to is_redirect?
* Add is_video?
* Add has_content? to confirm if response matches content
* Add redirected_to which yields redirected url on redirects
Add Entry conveniences and specs

* Delegate methods from request and response
* successful? predicate based on response.is_error?
* response_code alias for response.status