* First steps toward refactoring Statistical Distributions into smaller classes: BETA() and GAMMA() (and related functions) to start with... they all need a lot of tidying up, and more testing; but it's a start
* Add basic datatype validations to Beta and Gamma Excel function implementations
* Switch to using a trait with the validation methods to provide easier sharing between distribution classes
* Additional unit tests for Beta and Gamma functions, including unhappy path for validations
* Extract ChiSquared functions
* Additional argument validation checks with unit tests for Chi Squared functions
* Extract Fisher
* Move MEDIAN() and MODE() to the Averages class
* Extract filters for Median and Mode for common usage
* Merge branch 'master' of C:\Projects\PHPOffice\PHPSpreadsheet\develop with conflicts.
* New statistical tests
* Sniffs
* Additional statistical function unit tests
* Additional statistical function unit tests
* Fix case-sensitivity
* Fix HARMEAN code logic
* Unit tests refactored into individual files for all logical functions
Implemented IFNA()
* Fix silly typo
* NOT needs ...args to allow for test when no argument passed
* Codestyle
* Use instance asserts
Mark Baker