add a function gg_barbs to plot wind barbs

[PanfengZhang]

Tips for a helpful feature request:

In situations when draw wind vectors (or wind barbs) with python https://matplotlib.org/stable/plot_types/arrays/barbs.html#sphx-glr-plot-types-arrays-barbs-py, I would like to be able to draw wind vectors (or wind barbs) using ggplot2 and metR package. Can you add a new function gg_barbs in the metR package to implement this feature?

Thank you very, very much.

The wind vector illustration, which is drawed by matplotlib of python, is as follows:

[eliocamp]

Yes, adding barbs has been on the docket for some time (#162) but I haven't had the time yet to implement it.