support multi index
Fix #75 and #83 - pairs/nested hasAndBelongsToMany
Merge branch 'colprog-patch-2' into v1.1.1
Add test for multi index
Add test for the event `saving`

This test shows how to use the event `saving` to make sure a relation
is defined before saving the document.
Add test for validator
Fix some listeners s/on/once
Add test with innerJoin
Bump to 1.1.1