DescTools documentation for gamma, Somers' D and lambda

Primary package documentation for GoodmanKruskalGamma, SomersDelta and Lambda. The Details sections specify the tied-pair exclusion in Goodman and Kruskal's gamma, directional denominators for Somers' D, and modal-prediction interpretation of Goodman and Kruskal's lambda. These definitions corroborate mathematical interpretation; the documentation does not identify the implementation or version of an unspecified oii.xtab wrapper in a past examination.