Index time boosting is deprecated in Apache Lucene 6, and will be removed in Lucene 7.

While we currently are using Lucene 5, since we'll likely jump directly to Lucene 7 with the next major version of Hibernate Search, I think we should prepare our users already.

Let's deprecate @Boost and any option to control index-time boosting, so that people can start already to move to query-time boosting.