Added support for binary row annotations

Hi, Raivo
I've added support for row annotations with binary categorical variables. This is used in some of our research where we generate heat maps of samples on the columns and multivariate combinations of genes on the rows (such that each row represents some combination of genes that are either on or off, thus binary). The annotation on the rows reflect those combinations. This is generally useful for representing co-expression analysis from single cell data.
I've updated the documentation and so forth, the package passes R CMD check. Existing functionality is unchanged.
Best,
Greg Finak, PhD 
Staff Scientist, 
Fred Hutchinson Cancer Research Center