un_normalize: un_normalize
In snnR: Sparse Neural Networks for Genomic Selection in Animal Breeding

Internal function for going back to the original scale.

1	un_normalize(z,base,spread)

`z`	a vector or matrix with values are normalized between -1 and 1, this vector is obtained when normalizing a vector or matrix x.
`base`	if z is a vector, base is the minimum of x. if x is a matrix, base is a vector with the minimum for each of the columns of the matrix x.
`spread`	if z is a vector, spread=base-max(x). If x is a matrix, spread is a vector calculated for each of the columns of x.