Improved warm-up of new segments.

* Merged segments are now warmed-up at the end of the merge operation instead
  of _refresh, so that _refresh doesn't pay the price for the warm-up of merged
  segments, which is often higher than flushed segments because of their size.
* Even when no _warmer is registered, some basic warm-up of the segments is
  performed: norms, doc values (_version). This should help a bit people who
  forget to register warmers.
* Eager loading support for the parent id cache and field data: when one
  can't predict what terms will be present in the index, it is tempting to use
  a match_all query in a warmer, but in that case, query execution might not be
  much faster than field data loading so having a warmer that only loads field
  data without running a query can be useful.

Closes #3819
Remove extra 'processors' anchor in threadpool docs
Fix comment grammar
Support the `has_child`, `has_parent`, `top_children` queries (and filters) in other apis than just search api. The queries are also now supported in count, explain (return dummy explination) and delete by query apis.
Migrate SearchContext.Rewrite to Releasable. All the parent child queries are now implemented as Lucene queries and the state is kept in the Weight.
Completely disable caching for `has_child` and `has_parent` filters, this has never worked and it also can also never work. The matching docIds are cached per segment while the collection of parent ids is top level.

Closes #3822
Add monitoring link for es2graphite.
Added QueryBuilders#fuzzyQuery method that accepts value parameter as an object

Fixed javadocs

Closes #3616
Fix broken links in example configuration file
Doc values integration.

This commit allows for using Lucene doc values as a backend for field data,
moving the cost of building field data from the refresh operation to indexing.
In addition, Lucene doc values can be stored on disk (partially, or even
entirely), so that memory management is done at the operating system level
(file-system cache) instead of the JVM, avoiding long pauses during major
collections due to large heaps.

So far doc values are supported on numeric types and non-analyzed strings
(index:no or index:not_analyzed). Under the hood, it uses SORTED_SET doc values
which is the only type to support multi-valued fields. Since the field data API
set is a bit wider than the doc values API set, some operations are not
supported:
 - field data filtering: this will fail if doc values are enabled,
 - field data cache clearing, even for memory-based doc values formats,
 - getting the memory usage for a specific field,
 - knowing whether a field is actually multi-valued.

This commit also allows for configuring doc-values formats on a per-field basis
similarly to postings formats. In particular the doc values format of the
_version field can be configured through its own field mapper (it used to be
handled in UidFieldMapper previously).

Closes #3806
Fix GetIndexTemlatesRequest if serialized with includeAll and a old ES version
Add AssertingTransport that deploys basic BW-Compat serialization checks
Added an AwaitsFix to testDeleteAllOneIndex. Martijn is on it.
moved AwaitsFix to class level
Added IndexRequest#source(Object...) input validation

Added checks to IndexRequest#source(Object...) to ensure and even number
of parameters. This method otherwise throws an AIOOBException which is
confusing to users and doesn't report the root cause of the problem.
Fix small doc mistakes
[DOCS] Moved "named filters/queries" up one level
Enable Random TransportClients in tests
Add clear warnings that only the default codec, postings format and doc values format have backward compatibility warranties.
In the delete by query also acquire a searcher when shard state is RECOVERING and POST_RECOVERING
Add Random MergePolicy via index templates in integration tests

This commit adds support for random merge policies set for every
index created in an AbstractIntegrationTest. It will either set
'logbyte', 'logdoc' or 'tiered' merge policy as well as a random
value for compound files.
Fixed serialization error. POST_RECOVERY is now also serialized