Update named-queries-and-filters.asciidoc
[doc] Correct decay function equations in function_score description

Impact of decay and scale was missing from the equations.

Closes #6983
Fielddata: Fix the ordinals impl for sparse fields.

Caused by #6908
[DOCS] Fix nested root object indexing documentation

Types can no longer be specified when indexing, see:
https://github.com/elasticsearch/elasticsearch/pull/4552
Fielddata: goodbye comparators.

This commit removes custom comparators in favor of the ones that are in Lucene.

The major change is for nested documents: instead of having a comparator wrapper
that deals with nested documents, this is done at the fielddata level by having
a selector that returns the value to use for comparison.

Sorting with custom missing string values might be slower since it is using
TermValComparator since Lucene's TermOrdValComparator only supports sorting
missing values first or last. But other than this particular case, this change
will allow us to benefit from improvements on comparators from the Lucene side.

Close #5980
[TEST] Don't recycle in facets.

The recycling happening in facets is done manually and arrays are sometimes not
released. Aggregations do it in a less error-prone way by registering on to the
SearchContext.
Change numeric data types to use SORTED_NUMERIC docvalues type
instead of a custom encoding in BINARY.

In low level benchmarks this is 2x to 5x faster: its also optimized
for the common case where fields actually only contain at most one
value for each document.

Additionally SORTED_NUMERIC doesn't lose values if they appear more
than once, so mathematical computations such as averages are correct.

Closes #6967