[TEST] Use _uid sort field as tie, so that hits with the same score are sorted in the same way in both search responses.
More Like This Query: allow for both 'like_text' and 'docs/ids' to be specified.

Closes #6246
Update Documentation Feature Flags [1.2.0]
[SPEC] Removed the URL parameter `indices_boost` from the "Search" API

Related: elasticsearch/elasticsearch-ruby#29
Highlight fields in request order

Because json objects are unordered this also adds an explicit order syntax
that looks like
    "highlight": {
        "fields": [
            {"title":{ /*params*/ }},
            {"text":{ /*params*/ }}
        ]
    }

This is not useful for any of the builtin highlighters but will be useful
in plugins.

Closes #4649
[TEST] Don't stop master node.
[TEST] Just start two nodes
First prototype of the top_hits agg
Added builder, first test and more options to parsers
Added more tests
Added docs.