Added missing methods update_setting, optimize and alias to index and server.

I've added

 - index.update_settings (http://www.elasticsearch.org/guide/reference/api/admin-indices-update-settings/)
 - index.optimize (http://www.elasticsearch.org/guide/reference/api/admin-indices-optimize/)
 - server.get_alias (http://www.elasticsearch.org/guide/reference/api/admin-indices-aliases/)

The alias support is the /<index>/_alias/<alias> action to look up mappings based on an alias name or prefix.