mtorchiano/effsize: Minor changes and fixes

Marco Torchiano, Joses W. Ho, Etienne Gaudrain, Earcanal, Douglas Whitaker, Philipp & Giovani Guizzo
Fixed #41 #43 Merged branch single sample Choen.D #44 Merged three PR on documentation and typos: #42 #40 Also fixed a URL.
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