when parsing json, when we encounter the key "terms", we first
try to parse as traditional phrase query, then if that fails,
we also try parsing it as multi-phrase
the logic of how a phrase search works should be an internal
detail of the phrase searcher. further, these changes will
allow proper scoring of phrase matches, which require access
to the underlying searcher objects, which were hidden in the
previous approach.
This is a change in search result behavior in that location
information is no longer provided by default with search results.
Although this looks like a wide-ranging change, it's mostly a
mechanical replacement of the explain bool flag with a new
search.SearcherOptions struct, which holds both the Explain bool flag
and the IncludeTermVectors bool flag.
Boostable, Fieldable, Validatable broken out into separate
interfaces. This allows them to be discoverable when
needed, but ignorable otherwise. The top-level bleve package
only every cares about Validatable and even that is optional.
Also, this change goes further to make the structure names
more reasonable, for cases where you're directly interacting
with the structures.
