Performs a 1way ANOVA.
The oneway ANOVA tests the null hypothesis that two or more groups have the same population mean. The test is applied to samples from two or more groups, possibly with differing sizes.
Parameters :  sample1, sample2, ... : array_like


Returns :  Fvalue : float
pvalue : float

Notes
The ANOVA test has important assumptions that must be satisfied in order for the associated pvalue to be valid.
If these assumptions are not true for a given set of data, it may still be possible to use the KruskalWallis Htest (`stats.kruskal`_) although with some loss of power.
The algorithm is from Heiman[2], pp.3947.
References
[R172]  Lowry, Richard. “Concepts and Applications of Inferential Statistics”. Chapter 14. http://faculty.vassar.edu/lowry/ch14pt1.html 
[R173]  Heiman, G.W. Research Methods in Statistics. 2002. 