1. Write a function that takes as parameters a matrix and its dimensions,
and returns a NULL-terminated array of pointers to those matrix lines
that have at most one change in monotonicity (i.e., a line that is
decreasing up to a point, and then increasing, or the opposite).

2. Write a function that takes as parameters a matrix and its dimensions,
and returns a matrix that has as lines all colums of the original matrix
that are monotonic sequences.