Note: This breaks backward compatibility
* Removed clear/all parameters, now all stats are returned by default
* Made the metrics part of the URL
* Removed a lot of handlers
* Added shards/indices/cluster level paremeter to change response serialization
* Returning translog statistics in IndicesStats
* Added TranslogStats class
* Added IndexShard.translogStats() method to get the stats from concrete implementation
* Updated documentation
Closes#4054
Stats can be retrieved on a per-feature / per-component basis including the fields
they apply to. This commit add support for a 'completion' flag to include statistics
for the complition feature as well as 'completion_fields' to only
include certain fields into the returned statistics.
To disambiguate between 'fielddata' and 'completion' fields this commit
uses 'fields' as the default inclusion filter for stats fields only used
if not dedicated '[completion|fielddata]_fields' paramter is provided.
Relates to #3522
Kevin Wang
Alexander Reelsen
Dan Everton
Simon Willnauer
Clinton Gormley