Gauss 0.2.8

- Collection.unique, return a set of unique values
97b8db8d01ea708208687d5aa1a3155fb8bb51a1

- Collection.split, binomial cluster function
242384e06e5efbcb35d3b3416c34dbe8310c8974

- Fix object extension and refactoring
https://github.com/wayoutmind/gauss/issues/14

- Power/general mean
8628696a103cc238506f541ebf2c018ff4ce8d00

- Sample statistics and increased test coverage