Add more descriptive error for dim(::Field)

Author: emikelsons

src/Rings.jl

@@ -285,6 +285,7 @@ function krull_dim(R::Ring)
   throw(NotImplementedError(:krull_dim, R))
 end
 
+dim(::Field) = error("The value of `dim` is ambiguous for fields, see `krull_dim`, `vector_space_dim` or `rank`.")
 krull_dim(::Field) = 0
 krull_dim(::Integers) = 1