Monoid Creation with Scalar

[rayegun]

Many functions now allow a Scalar argument in addition to the existing GrB_Function_<TYPE> functions that exist today. Several are missing though, including Monoid. These would be nice to have, and simplify the Julia wrapper in several places.

[DrTimothyAldenDavis]

That would be nice to add. Perhaps to the v2.2 C API?

In the v3.0 API, I'd love to see the GrB_Function_<TYPE> methods all disappear. Non-opaque C scalars are bad for fusion.