scikit-posthocs: v0.8.0

This release includes a number of features, enhancements and fixes:

• critical difference diagrams (see critical_difference_diagram) are implemented (thanks to @pedroilidio and @chengmingbo)
• outliers_gesd code improved (thanks to @ysBach)
• increased abs tolerance for Wilcoxon test (test_posthoc_wilcoxon)
• minor updates and fixes