Add exp and log linear algebra functions.

PR-URL: https://github.com/jstat/jstat/pull/112
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
Add cumreduce function

Add cumulative array/matrix sum and product in terms of cumulative
reduce.

PR-URL: https://github.com/jstat/jstat/pull/112
Reviewed-by: Trevor Norris <trev.norris@gmail.com>