Clarify comment on standard deviation util function.
Implement a class that generates a grid of Gaussian peaks whose envelope follows a sphere function.  This can be constructed by combining PinCushionSphere, SphereObjective, InvertedObjective, MaxObjective and ConstantObjective in a parameter file, but its far simpler to have it defined in advance in one object.  Added constructors to the relevant classes to allow them to be instantiated programmatically (rather than only via parameters).  Fixes #6.