Make sure the algorithm handles the possible input types correctly

[ssiccha]

The input matrix could be:

• a list of lists
• an Is8BitMatrixRep matrix
• a cvec cmat
• other IsMatrixObj objects?

The return values should be an Is8BitMatrixRep matrix in the first two cases and a cvec cmat in the third case.

Make sure to document that using the cvec package should be more efficient.