Introduce "@not_supported" decorator

[guilhermeleobas]

From #453 (review)

While implementing and documenting Array API in the HeavyDB context, I think we should clearly distinguish the "Not implemented" and "Not supported" cases. The "not implemented" means that the corresponding feature can be implemented if taken some time for it, while "not supported" means that the corresponding feature does not makes sense because the underlying datastructures do not support it. For instance, OmnisciDB currently is able to support only 1-D arrays, and hence, we should not give hope to users that inherently N-D operations such as matrix operations can be supported via raising an rbc issue.