this is a prerequisite for command instance management:
We have now an (almost) complete framework for writing actual
command definitions in practice, which will be registered automatically.
This could be complemented (future work) by a script in the build process
to regenerate proc/cmd.hpp based on the IDs of those automatic definitions.
as it stands, this does not work, since lambdas are passed by-value,
while function references can only be passed by explicit reference,
otherwise they'll degrade to a function pointer. And std::function
requires a plain function signature as type argument, not the type
of a function pointer (which doesn't mean you can't construct a
std::function from a FP, indeed there is an explicit overload for
that).
