Create a matrix filled with zeros.
	zeros(3)
| h | Height of the matrix. | 
| w | Width of the matrix (optional). If not given, assumed to be the same as the height. | 
| return value | A matrix filled with zeros. | 
The numbery of parameters can vary:
0 - Returns 0.
1 - Returns a square matrix with size determined by the argument.
2 - Returns a rectangular matrix with size determined by arguments.