Merge pull request #27 from Obvious/jeremy-bugs

Adding better error checking for missing args. in parent
Adding fix for turning subgraphs into modifiers
Adding extra check in graph nodes to make sure the node name didnt change for modifiers
Handling case where an input has been remapped
Whoops
Fixing recursing
Merge pull request #28 from Obvious/jeremy-modifierSubgraphs

Adding ability to use subgraphs as modifiers
Added ability to retrieve the handler function for a node
Merge pull request #29 from Obvious/jeremy-handlers

Adding ability to retrieve the function for a given graph node
Adding support for disabling of callbacks
Adding more commenting to callback test
Merge pull request #30 from Obvious/jeremy-promisesOnly

Adding support for disabling of callbacks
Update package.json
Fixing subgraphs to work with disabling of callbacks