* Issue 2066, highlighting more validation needed for LookupRef Functions * Additional test cases
* 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
Allow to use cell references as row and column in function INDEX(). Eg: ``` =INDEX(A1:B5, A9) ```