Traits for rings and fields

Don't have to implement anything extra beyond usual arithmetic traits, but may want to.

• Add<Output = Self>

• Sub<Output = Self>

• Neg<Output = Self>

• Mul<Output = Self>

• Eq

• From

• Sized

• Div<Output = Self>

• Commutative

Commutative being only a marker trait to say that we are relying on the multiplication being commutative.

LazyLinear<N, T> covers formal linear combinations of T with coefficients in N.

One can add, negate, subtract, multiply by constants convert from T and (N,T).

If T implements a TermMultiplier for how it gets multiplied with a T2 to produce a linear combination of T's and T2 does for how it gets multiplied with a T2 to produce a linear combination of T2's then one can multiply LazyLinear<N,T> and LazyLinear<N,T2> where the former is the module for the later which is an algebra.

uses bitvec to cram entries together