Add  method and test
Change transaction promise to resolve snapshot instead of snapshot.val
pass key of into 'on change' callback. fixes #216

pass key of changed child into 'on change' callback. fixes #216
Update bower.json - Fix missing quote
Merge pull request #218 from apai4/patch-1

Update bower.json - Fix missing quote
Merge pull request #217 from tomsaffell/fixes

pass key of into 'on change' callback. fixes #216
Merge pull request #215 from mikepugh/master

Add support for transaction method via $transaction