Update docs for pow_fps.
Update docs for pow_fps.

fredrik-johansson/flint2,dsroche/flint2,wbhart/flint2,wbhart/flint2,fredrik-johansson/flint2,dsroche/flint2,dsroche/flint2,fredrik-johansson/flint2,wbhart/flint2,dsroche/flint2