Interface for external compilers #316
Description
This feature enhancement is related to issue #312 which focuses on extending the pygsti implementation of DRB to benchmarking general universal gate sets. A required ingredient for this is the ability to compile unitary operations out of a given universal gate set, and rather than build out such a compiler from scratch the current plan is to build out an interface to external compilers that would allow users to use their own compiler (with the potential option of a default external compiler we use). This functionality is of broader utility than just generalizing DRB, however, so spinning this out into a separate feature thread.