plot_2D: Generate x-y scatter plots.
In NESCent/MINOTAUR: MultIvariate visualisatioN and OuTlier Analysis Using R

Generate x-y scatter plots with outliers overlayed. Easily control the aesthetics of plot scatter and outlier points.

plot_2D(x, y, xlab = NULL, ylab = NULL, xlim = NULL, ylim = NULL,
  n.bins = 100, col.pal = "heat.colors", grid = FALSE, outlier.x = NULL,
  outlier.y = NULL, outlier.col = "blue", outlier.col.bg = "purple",
  outlier.transp = 0.25, outlier.pch = 24, outlier.cex = 1.5)

`x`	A numeric vector containing a variable to be plotted along the x-axis of the xy scatter.
`y`	A numeric vector containing a variable to be plotted along the y-axis of the xy scatter.
`xlab`	An optional character string specifying a label for the x-axis.
`ylab`	An optional character string specifying a label for the y-axis.
`xlim`	An optional numeric vector of length 2 specifying limits for the x-axis.
`ylim`	An optional numeric vector of length 2 specifying limits for the y-axis.
`n.bins`	An integer specifying the number of bins for the xy scatter pixels.
`col.pal`	A character string specifying the color palette to be used for the xy scatter pixels.
`grid`	A logical specifying whether to overlay a grid on top of the plotting area.
`outlier.x`	An optional numeric vector giving the x-coordinates of an outlier to be plotted as points.
`outlier.y`	An optional numeric vector (required if outlier.x is provided) giving the y-coordinates of an outlier to be plotted as points.
`outlier.col`	A character string specifying the color of the outline of the outlier points.
`outlier.col.bg`	A character string specifying the background (fill) color of the outlier points.
`outlier.transp`	A number between 0 and 1 specifying the degree of transparency to be added to the outlier points.
`outlier.pch`	A number between 21 and 25 specifying the shape of the outlier points. (See ?par for details.)
`outlier.cex`	A number specifying the cex (size) of the outlier points.