Remove conversion of collections without broadcasting

This removes one of the original features which can be useful when using this as a kind of calculator. It now seems more important to bring the interfaces into line with what Unitful.jl. offers, at the cost of adding a '.' here and there.

Also, promote_to_derived is now exported. This removes one of the many things to remember when writing glue code for other packages (GluecodeDiffEqBase).