Support bounds for mrmatrix

[mccalluc]

pete says:

In the future, it should work like in npmatrix. The reasoning: a matrix, as implemented programmatically is necessarily a 2D array whose indices go from (0, 0) to (len-1, len-1). Imagine that we want that matrix to represent rasterized values for a geographical region. Bounds would indicate the upper left and lower right corner latitude, longitude pairs for the rasterized region. So you could have a 1000,1000 matrix represent a region that goes from (10 degrees,10 degrees) to (10.1 degrees, 10.1 degrees), for example.