completed the function 'diagonal' that returns the kth diagonal of a rectangular matrix, added function in PMatrixSubComponents protocol, default implementation and tests.
(does not handle k values that are out of range)
completed function diagonal, added function in PMatrixSubComponents protocol, default implementation and tests.
(does not handle k values that are out of range)
function 'diagonal' had a bug, it was calling (mp/main-diagonal [m]) instead of (mp/main-diagonal m)
undid addition of 'kth-diagonal', bug fix still implemented
Merge pull request #106 from prasant94/develop

Bug in the function 'diagonal'.