Remove gap-only columns from blocks. This does not modify coordinates and might be necessary after a
maf.filter= \ [...], XFullGap( species=(species1,species2,etc)), \ [...]
species=(species1, species2, etc)
A coma separated, within parentheses, list of species. Any column containing a gap in the specified species will be removed. If other species are present in the block, the corresponding character will be removed, whether it is a gap or not. The coordinates of these species will then be discarded.