Move mean/linspace from SGVector to CStatistics/CMath respectively

@iglesias Turned out that `SGVector::linspace_vec` was being used at one place, so I didn't remove it.
Yeah, I guess also it stems for cumulative sum. In any case, I understand
the cumulative sum (cumsum, for short I'd use) is an array that behaves
like the cdf for a pdf. This is just a single value so sum makes more sense
to me.
On 21 Dec 2014 09:32, "Sanuj Sharma" <notifications@github.com> wrote:

> In src/shogun/mathematics/Statistics.h
> <https://github.com/shogun-toolbox/shogun/pull/2649#discussion-diff-22146482>
> :
>
> > @@ -39,7 +41,16 @@ class CStatistics: public CSGObject
> >  	 * @param values vector of values
> >  	 * @return mean of given values
> >  	 */
> > -	static float64_t mean(SGVector<float64_t> values);
> > +	template<class T>
> > +		static floatmax_t mean(SGVector<T> vec)
> > +		{
> > +			floatmax_t cum = 0;
>
> @iglesias <https://github.com/iglesias> yeah even i noticed this :-D but
> then I thought it might mean 'cumulative' or something like that. Anyways,
> I'll change it and make it sum.
>
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> <https://github.com/shogun-toolbox/shogun/pull/2649/files#r22146482>.
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