Added the API definition for checking the document type existence
Added the API definition for `_flush`
Added the API definition for `_gateway/snapshot`
Added the API definition for deleting a document type
Added the API definition for `_mapping`
Added the API definition for updating the mapping
Added the API definition for opening an index
Added the API definition for `_optimize`
Added the API definition for `_refresh`
Added the API definition for `_segments`
Added the API definition for `_settings`
Added the API definition for `_stats`
Added missing URL parts for the `_stats` API
Added the API definition for `{index}/_status`
Added the API definition for deleting an index template
Added the API definition for getting an index template
Added the API definition for creating or updating a template
Removed the incorrect "required" for index in the `_settings` API
Added the API definition for `_validate/query`
Added the API definition for deleting a warmer