Closes#396
This removes `PartialOrd` and makes `BaseNum` and `BaseFloat` simple trait aliases. This should allow more types to be used as parameters in the cgmath data types at the expense of removing `Array::min` and `Array::max`.
This adds `Sum` trait for the `MatrixN`, `VectorN`, `Quaternion`
structures and the `Product` trait for `MatrixN`, `BasisN` and
`Quaternion`.
It also add constraints on the `Rotation` and `SquareMatrix` to require
the `Product` trait and `VectorSpace` to require `Sum`.