[TEST] clarified skip features usage
Add explanations for all AllocationDeciders

Relates to #4380
Relates to #2483
Remove support for boost in copy_to field

Currently, boosting on `copy_to` is misleading and does not work as originally specified in #4520. Instead of boosting just the terms from the origin field, it boosts the whole destination field.  If two fields copy_to a third field, one with a boost of 2 and another with a boost of 3, all the terms in the third field end up with a boost of 6.  This was not the intention.

  The alternative: to store the boost in a payload for every term, results in poor performance and inflexibility. Instead, users should either (1) query the common field AND the field that requires boosting, or (2) the multi_match query will soon be able to perform term-centric cross-field matching that will allow per-field boosting at query time (coming in 1.1).
Don't load CompetionTerms if lookupFactory is null

Closes #4970
Closes #4788
Prevent usage of object based RamUsageEstimator in Completion090PostingsFormat
Add RamUsageEstimator#sizeOf(Object) to forbidden APIs

This method can be a performance trap since it traverse the
entire object tree that is referenced by the provided object.
See LUCENE-5373
Added `fields` support to `geo_point` and `completion` field type.

Upgrading 0.90.x `multi_field` type that has a `geo_point` or `completion` field type as default field would otherwise fail.
Also it make sense to support these field types, because both support specifying the actual values as string.
Parent / child queries should work with non-default similarities
[TEST] Added check that yaml REST test suites always end with \n

Our yaml parser seems to be too tolerant in some cases, e.g. it properly parses yaml suites when they don't end with a line feed, whereas other clients tests break due to that. We should try to do the same to keep consistency across runners.
[TEST] Added ability to test apis that don't return json

The last response body gets now always stashed in the REST tests and can be retrieved via `$body`. This implies that not only expected values can be retrieved from the stashed values, but actual values as well.
Added support for regular expressions to `match` assertion, using `Pattern.COMMENTS` flag for better readability through new custom hamcrest matcher (adopted in do section as well).

Added also example tests for cat count api