Some attributes

[Don]

bearophile wrote:
> Few new attributes that can be invented:
> @nocommutative, to "disable" the commutativity of an operator overloading, like + or *, so it becomes like the + and * of floating point values. It's useful for example if you want to implement Clifford algebras. With the new operator overloading regime it becomes a less easy to design this attribute.

The new operator overloading doesn't have commutativity by default, so 
we don't need this (BTW + and * are commutative in floating point, it's 
associativity that doesn't hold).