Allow plot_scan1_circ() to plot points rather than lines, and
use altcol argument to have alternative chromosomes in different
colors.
Add package logo
Add arguments col and add to plot_scan1_circ(), and allow
better handling of ... with an internal function.
Add examples for plot_scan1_circ() and xy2circ()
Make output of xy2circ() a data frame
lwd to plot_scan1_circ().plot_scan1_circ() and xy2circ()