Random Node Creation and Node Macro Merge/Cleanup

[ostrosco]

• Created two new nodes: NormalNode and UniformNode to generate normal and uniformly distributed random numbers.
• Added support for creating node with generic input types.
• Merged aggregate node creation into create_node to reduce number of macros required to create node. This does have the side effect of not allowing Option types to be sent through the channels, but I don't think this is a common use case at all.
• Re-factored common code from the macro into sub-macros to increase readability and maintainability.

This shouldn't break existing nodes who were using create_node!. If a node was using create_aggregate_node!, renaming the macro call to create_node! provides similar functionality.

[ostrosco]

Got two reviews, so I'm gonna go ahead and merge it up.