Usage
circos.trackText(factors, x, y, labels, track.index = get.cell.meta.data("track.index"),
direction = NULL, facing = c("inside", "outside", "reverse.clockwise", "clockwise",
"downward", "bending", "bending.inside", "bending.outside"), niceFacing = FALSE,
adj = par("adj"), cex = 1, col = par("col"), font = par("font"))