===========
- Modified 'error_components' method so that if 'pprint=True', nothing is
returned.
- Added pickling functionality (an object's before and after counterparts are
not yet correlated, but objects unpickled together maintain prior
correlations)
- Updated display of class objects from "UF(...)" and "UV(...)" to simply
"uv(...)" for both and created an auxiliary method "describe" to provide a
textual explanation of the distribution moments (i.e., "Mean...",
"Variance...", etc.)
- Corrected a bug in the "error_components" method that caused the cross-product
components to point to the linear components
- Removed "raw2central" utility function from being imported automatically since
it is mostly used in internal calculations anyway.
- Added more documentation to class methods/functions
- Added ``covariance_matrix`` and ``correlation_matrix`` methods.