Improve Code Climate score of Distribution::MathExtension

[agarie]

As can be seen in Code Climate, the worst scores of Distribution are located in the MathExtension module and the modules inside it.

Since Ruby has some new functions in its Math module, we should try to come up with ways to simplify things; maybe we can improve MathExtension by removing code from it.

Another option is creating a gem for special functions (name needed) that would handle these things and could also be used in Minimization, Integration, &c. (ideally with C implementations for speed)