[Docs] Added a page for the Perl client
[Docs] Typo
Added generic cluster state update ack mechanism

Added new AckedClusterStateUpdateTask interface that can be used to submit cluster state update tasks and allows actions to be notified back when a set of (configurable) nodes have acknowledged the cluster state update. Supports a configurable timeout, so that we wait for acknowledgement for a limited amount of time (will be provided in the request as it curently happens, default 10s).

Internally, a low level AckListener is created (InternalClusterService) and passed to the publish method, so that it can be notified whenever each node responds to the publish request. Once all the expected nodes have responded or the timeoeout has expired, the AckListener notifies the action which will return adding the proper acknowledged flag to the response.

Ideally, this new mechanism will gradually replace the existing ones based on custom endpoints and notifications (per api).

Closes #3786
Put warmer api to support acknowledgements

Added support for acknowledgements in put warmer api using the generic mechanism introduced in #3786

Closes #3831
Delete warmer api to support acknowledgements

Added support for acknowledgements in delete warmer api using the generic mechanism introduced in#3786

Closes #3833
Added simple count down class that allows to be fast forwarded

Closes #3910
Prohibit indexing a document with parent for a type that doesn't have a `_parent` field configured and prohibit adding a _parent field to an existing mapping.

Closes #3848 #3849
[Docs] added document for the lenient option in match queries
[Docs] updated refrences to dynamic_date_formats
Added initial documentation for the redesigned percolator.
[Docs] update reference to remove documentation about percolating during an index, bulk or update request.
Added brief overview of the python client to the guide
Added a link to official Python client to the client list, fixed perl link
Terms facet will now throw a parsing exception if no field, fields or a script is supplied.

Previously you'd get an NPE. Also added extra exception when called with unknown parameters.
Java API Documentation (0.90+) needs update for accessors in Facets docs
Closes #3921.
(cherry picked from commit a753c48)
[DOCS] How to check max_file_descriptors
Settings queue_size on index/bulk TP can cause rejection failures when executed over network
The #3526 fix was not complete, it handled cases of on node execution, but didn't properly handle cases where it was executed over the network, and forcing the execution of the replica operation when done over the wire.

This relates to #3854

closes #3929
Fix teh typos in javadocs
phrase_len is not called phrase_length
Allow awareness attributes to be reset via the API

Currently we don't allow resetting the awareness
attribute via the API since it requires at least one
non-empty string to update the setting. This commit
allows resetting this using an empty string.

Closes #3931