Functions for taking the mean and standard deviation of an array of numbers?

I've been thinking about how to help Arduino users do more sophisticated analysis of their sensor data and this seems like a simple thing that could help with a bunch of things. There are some existing libraries for this (e.g. http://playground.arduino.cc/Main/Average) but it seems like mean() and standardDeviation() are common enough to be worth including in the core. What do you think?

No files, tests, or entry points are named. Start by reviewing the ArduinoCore-API organization and existing core APIs, then determine the appropriate array interface, numerical behavior, and tests needed before deciding what a complete addition would entail.

Written by the indexing model from the issue text.