hlaSNPGenoClass: The class of SNP genotypes
In HIBAG: HIBAG -- HLA Genotype Imputation with Attribute Bagging

The class of SNP genotypes, and its instance is returned from hlaMakeSNPGeno.

There are five components:

`genotype`	a genotype matrix, “# of SNPs” - by - “# of individuals”
`sample.id`	a vector of sample IDs
`snp.id`	a vector of SNP IDs
`snp.position`	a vector of SNP positions in basepair
`snp.allele`	a vector of characters with a format of “A allele/B allele”
`assembly`	the human genome reference, such like "hg19"