Added some utility metric helper functions

Implementation for  Issue #32 .

As the ticket is unclear of any type of helper methods than "normal distribution" I was not sure what to implement.

I personally don't know if these types of methods need to be in here, as they are very simple and use case specific for how someone would use metrics.  These might be better off in a wiki page showing examples of some of the things that could be done with metrics so that they can include it in their own code base if they need it.