Add M × N matrix : vector subtraction support

[chrissimpkins]

Requirements:

Left hand side Matrix and right hand side Vector must have the same row and column dimensions.

Properties:

anti-commutative: A - B = -(B - A)
non-associative (order of subtraction operations matters)
subtraction with additive identity matrix (zero matrix) yields the same matrix

Questions:

• how do we approach the Vector shape? Always a column vector?