Convert operator arguments to references, const correctness. #161
Change in to input for ControlGenerators for consistency
Signal flow operator takes const RHS reference, returns new copy of rhs with input
Revert "Convert operator arguments to references, const correctness. #161"

This reverts commit cb83fef67deaf35114db2e2c70525a0c1d2612f8.
Pass by value and return by value for all operators, errywhur. #161
Remove a few more pass-by-references
Merge pull request #162 from TonicAudio/ND-OperatorReferences

Remove all pass-by and return-by-reference