order of moment

1-order moment http://en.wikipedia.org/wiki/Moment_%28mathematics%29
2-order skewness http://www.uib.no/People/ngbnk/kurs/notes/node34.html
4-order kurtosis http://www.uib.no/People/ngbnk/kurs/notes/node35.html
http://pygsl.sourceforge.net/reference/pygsl/node31.html