SetSort::at should return based on the sort
Make Set::at observable
document Set::at and SetSort::at
don't document Set::at
SetSort::at updates when items are modified
SetSort::toArray updates when order changes
support addArray on transactionAssociationSet
support removeArray with transactionAssociationSet
Merge pull request #1109 from batmanjs/set-sort-at

SetSort::at should return based on the sort
Merge pull request #1111 from batmanjs/transaction-addArray

support addArray / removeArray on transactionAssociationSet
Better missing controller error message (fixes #613)
Merge pull request #1113 from batmanjs/no-controller-message

Better missing controller error message (fixes #613)
Merge branch 'master' into assoc-docs