Issue with addTextLabels: Add srt and xpd as parameters

As a feature request, would you be able to add support for the 'srt' and 'xpd' graphical parameters to your `addTextLabels()` function? I browsed through your code, but wasn't sure how one would calculate the heights and widths of the labels... (for srt, I supposed you could calculate the height and width as you do and then rotate the xMarkers and yMarkers values by the specified angle).