2018-02-08: Release of version 1.3.1:
   Fixing memory leak, functionality unchanged.
2018-01-09: Release of version 1.3.0:
   Speed up of core ECF code, functionality unchanged.
2016-10-07: Release of version 1.2.0:
   Incorporates the generalized energy correlation functions
   and adds the NSeries, MSeries, USeries, and GeneralizedD2
   observables.
2014-11-13: Release of version 1.1.0:
   Added the C1, C2, and D2 observables
2013-05-01: Release of version 1.0.1:
   Improved error reporting
2013-04-30: Release of version 1.0.0:
   Initial release
