A character strings specifying column alignments, defaulting to
paste(rep('c',ncol(x)),collapse='') to center. Valid alignments are
l = left, c = center and r = right. You can also specify align='c|c' and
other LaTeX tabular formatting. If you want to set the alignment of the
rownames this string needst to be ncol(x) + 1, otherwise it automatically
pads the string with a left alignment for the rownames.