Breaking Changes

1. Fix#521 - Fundamentally redesign ofquantile_normalize() to use a more efficient
   algorithm. This has resulted in a breaking change as the output is now slightly
   different. The new algorithm is also faster and more memory efficient.

New Features

1. Fix#510 - Add parameter totidy_mixture_density() to allow for different
   types of combinations, add, subtract, stack, multiply and divide.

Minor Fixes and Improvements

None