#' Usage: ggplot(...) + geom_X(...) + pointsPutX(...)
pointsPutX(x_range, x_section, y, col = NA)
[min,max] valid range of x-values
[min,max] fraction in which to distribute the values (in [0,1] for min,max, e.g. c(0.03,0.08) for 3-8%)
Y-values
Colour of the points (used as argument to aes(colour=))
ggplot object with new geom_point