belongs_to associations can specify columns
Refactor: Extract selected_columns and associated_columns
Refactor: Extract columns and subquery_sql
Add nested includes and column select for has_many
Fix transactional tests
Extract JSON query classes to there own files
Add all_json method
Add specs for include has_many conditions and order
Add has_and_belongs_to_many assocation support
Fix empty array associations
Refactor association scope builder
Add conditions support to belongs_to
Added JSON generation benchmarks
Bump version to 0.4.0