Pycloudflare

* Add modelling and service methods for PageRules.

* Remove `pycloudflare.pagination`, in favour of Demands' pagination.
* Switch to 1-based indexing. Previously, page 0 and 1 would have
returned the same content, leading to some duplication in results.

* Add `models.Zone.get_ssl_verification_info` method.
* Add `services.CloudFlareService.get_ssl_verification_info` method.

* Add `models.Zone.purge_cache` method (and corresponding service support).

* Add `models.User.create_cname_zone` method.

* Add `services.CloudFlareHostService.zone_set` method.