Core Drupal Search Architecture for D8

Look at search, search_api, solr, Lucene API, and other contrib search-related modules. Come up with a proposed architecture that would be more modular than the current core search module, combining elements from existing modules, and building a framework that the existing contrib modules could connect to and use rather than fight against.

We would also need to provide a default search back-end in core, which could either be the current database-based back-end of the core search module, or the Zend framework's PHP lucene implementation. Core should also provide a framework for facet blocks, sorting, etc, that can be leveraged by all the back ends.