Version 2.9.0

Changelog

• Feature: Added Query::asKeyword() helper to resolve a field name with the .keyword suffix, which is used to cast a field to a static keyword value to be used in term queries or aggregations. It really doesn't do anything else; this just makes code easier to read and less typo-prone (think Query::asKeyword(Model::CATEGORY) instead of Model::CATEGORY.'.keyword').