row and column operations

The usual row and column operations apply to mutable matrices. These are:

• rowAdd -- add a multiple of one row to another
• rowSwap -- interchange rows
• rowPermute -- permute some rows
• rowMult -- multiply a row by a ring element
• rowDivide -- missing documentation
• columnAdd -- add a multiple of one column to another
• columnSwap -- interchange columns
• columnPermute -- permute some columns
• columnMult -- multiply a column by a ring element
• columnDivide -- missing documentation