Add M × N Matrix : Matrix multiplication support

[chrissimpkins]

Requirements:

for matrices A (=lhs) and B (=rhs):

• the column number in A must match the row number in B

Properties

for matrices A, B, and C:

• not commutative: AB ≠ BA)
• associative: (AB)C = A(BC)
• left distributive: A(B + C) = AB + AC
• right distributive: (B + C)A = BA + CA
• multiplication by zero matrix yields zero matrix: A0 = 0A = 0