Fix handling of stop word _lang_ notation

Fixes #2412
 #2436 expose KeepWordTokenFilter by default
Add basic javadocs for o.e.cluster.rounting package and related classes
fix sporadically disappearing fields during concurrent dynamic mapping updates
cleanup docsets
- remove the DocSet abstraction, and use Bits where we can by getting it from DocIdSet
- better handling of acceptDocs, though still need to properly apply them when caching is involved
The relevancy score in explanation should match the actual score in custom_filters_query

Fixes #2441
Add types and stats to search slow log
closes #2455
no need to check for log levels
we already do that when we log, and those are set to TRACE most times for slow log (since logging is based on thresholds)
Upgrade to Netty 3.5.11
closes #2456
Indexing Slow Log
closes #2457
Deprecate Shared Gateway
closes #2458
remove snappy support
relates to #2459
Fixed unable to highlight on all multi-valued field values.
Closes #2384
not delete filter improvements
- don't check no null for liveDocs, since we know they are not null with the check for hasDeletion
- improve iteration over liveDocs vs. innerSet, prefer to iterate over the faster one
add 0.19.13
fix properly handling acceptDocs in filters
our idea is to apply it on the "filtered/constant" level, and not on compound filters, so we won't apply it multiple times. The solution is conservative a bit now, we can further optimize it in the future, for example, not to wrap it when no caching is done within the filter chain
expose filter strategy in filtered query
add a marker CachedFilter
this allows to easily and globally check if we cache a filter or not, all filter caching uses this marker interface
Expose fragmenter option for plain / normal highlighter.
Closes #2465
Expose es version in node info api.
Closes #2466