Added supported types constant and #markup, #markup_create methods to provider.
Created #markup and #markup_create methods in Provider::Desk.
Added json markup for all supported types for desk (incl. create) and zendesk (excl. create).
Added a supported types map to Provider::Zendesk.
Added a #markup method to Provider::Zendesk.
Changed auths factory to support zendesk auth.
Added a provider spec to cover all provider methods.

This commit fixes #31 with 100% code coverage.