Add Helpers::CSV module to DRY up some common CSV stuff
Let ResultSet be usable by itself
Allow passing a score/match set directly into Configuration.new
Don't allow per-set options in ResultSets::CSV
Rename :database option to :conn in Database-related sets
Improve database-related sets

- add database helper module
- remove per-set customization in ResultSets::Database
- unify connection options across sets