[API] Remove "Snapshot Index" API

Related: elasticsearch/elasticsearch@3ffd0a1
[API] Add the `force` option to the "Optimize" API
[API] Added documentation for new options for the `version_type` argument

Related: elasticsearch/elasticsearch@b7a95d1
[API] Added documentation for the `metric` argument in the "Cluster State" API

Related: elasticsearch/elasticsearch@4fe6952
[API] Updated the "Index Stats" API to the current implementation
[API] Added the `human` parameter to COMMON_QUERY_PARAMS
[API] Added the "Snapshot Status" API

Related: elasticsearch/elasticsearch#4946