exclude assertions from coverage
Coverage of Query.prefetch()
Merge branch 'master' to 'orm': better coverage
Renaming of internal class: Index -> DBIndex
Local variable renaming: indexes -> cache_indexes
Minor refactoring
Refactoring: internal class Index is introduced
Use list instead of dict for Entity._indexes_
Fixes #88: composite_index(*attrs) added to support non-unique composite indexes
Merge branch 'master' to 'orm': non-unique composite indexes