Add highlighting support for suggester.

This commit adds general highlighting support to the suggest feature.
The only implementation that implements this functionality at this
point is the phrase suggester.
The API supports a 'pre_tag' and a 'post_tag' that are used
to wrap suggested parts of the given user input changed by the
suggester.

Closes #3442
Add binary protocol backwards compatibility for suggest highlights

This change requires different request processing on the binary protocol
level since it has been we provide compatibilty across minor version.
Yet, the suggest feature is still experimental but we try best effort
to make upgrades as seamless as possible.