Add a general purpose perform_function

[emgre]

It should accept just a function code and request headers. It could be used for class assignement or to freeze counters for example.

See https://github.com/dnp3/opendnp3/blob/097b6ddcb012a54c9e8e10db03fec98ddc898341/cpp/lib/include/opendnp3/master/IMasterOperations.h#L150-L153

[jadamcrain]

This caused a lot of confusion in retrospect for OpenDNP3 since it only works for requests that don't return data, it's pretty limited in what it can do.