Translate Nodes to Inherit from an "ISPNGNode" (Can think of a better name)

[calcuttj]

This will be a class to be inherited by SPNG Nodes. It can serve several purposes

1. Determining if the necessary TorchTensors exist within the input TorchTensorSet
2. Stripping away any irrelevant TorchTensors within the input
3. Batching/unsqueezing the TorchTensors if necessary
4. Communicating with the Device interface
5. Communicating with the Semaphore

class ISPNGNode: 

virtual bool operator()(const input_pointer& in, output_pointer& out) final;
virtual bool execute()(const input_pointer& in, output_pointer & out) = 0; //Pure virtual -- must be implemented by concrete class
...

bool operator()(const input_pointer& in, output_pointer& out) {
  ...common_operations...
   execute(...)
  ...common_operations...
} 

[brettviren]

We'll need a small handful to of such base classes to populate the different INode types we implement. At least SPNGFunction and SPNGFanin and SPNGFanout.

BTY, in the case of the last two, they can be useful on their own. Eg they may provide a nonvirtual but no-op execute() implementation. They can work generically once we implement the SPNG tensor data model. In cases where we want a node that both fans and performs some operation, those nodes can inherit and override execute(). In some cases, perhaps still benefit by calling the default execute().

[brettviren]

In the SPNG TDM paradigm, a FunctionNode (no torch operations) and TorchFunctionNode (for Torch operations) is the primary base class for "user" code but also offers standard, configurable operations on their own. The FaninNode and FanoutNode are generic and mostly not meant to be subclassed (but can in a pinch).