add class prediction error plot

[bhishanpdl]

This is just a heads up for the programmers that this is a dead library and it functionalities may break any time.
There has been not a single update form 2018 and most probably there will be no bug-fix or feature implementations.

Either implement your own plotting functions or look at other active modules such as yellowbrick.

scikit-plot is dead and it might break any time, if you use this in production.