Added multiple-component query with tests
Merge branch 'multiple_component_query' into integer-entity

There is a performance benefit in using integers as entity IDs instead
of full-blown Entity classes. This is particularly noticeable in the multiple
component queries. In the future the Entity class can be used maybe as
syntactic sugar (see the ebs module for comparison), but there is no
technical reason to use it solely to encapsulate GUIDs.