Identity matrix inserter for multiple rows

[dwysocki]

Expand diagonalizer.r to insert multiple copies of the identity matrix. Right now it inserts an nxn identity matrix when given an nxm table. Add an optional argument to provide the n used for the identity matrix as a parameter, and if n is less than the number of rows, repeat the identity matrix multiple times vertically. If n does not divide the number of rows, throw an error.