* Start work on array-enabling the Lookup and Reference functions
Requires a new method (`evaluateArrayArgumentsSubsetFrom()`) in the `ArrayEnabled` Trait to handle functions where the arguments that need special array handling are trailing rather than leading arguments
* Extract LookupRef\INDEX() into index() method of LookupRef\Matrix class
Additional tests
* Bugfix for returning a column using INDEX()
* Some improvements to ROW() and COLUMN()
* Simplify some of the INDEX() logic, eliminating redundant code
Mark Baker
Maxim