geno is a class union of several matrix-like types, many of
them suitable for very large datasets.
Currently supported are LinkedMatrix, BEDMatrix,
big.matrix,ff_matrix, and matrix.
LinkedMatrix-class,
BEDMatrix-class,
big.matrix-class, ff, and
matrix for more information on each matrix-like type.
BGData-class for more information on the BGData class,
in particular its geno accessor that accepts geno objects.