Please add a feature to vary the thickness of the line in Geom.line and Geom.path

[arinbasu]

Geom.line and Geom.path are widely used for a range of different visualisations. Both these features can gain if a line thickness or linesize parameter is added to the function. Can you please add a linesize parameter, such that we could do something like
Geom.line(size = somevalue) OR
Geom.line(size = :some_variable)
and depending in the value of the variable, the thickness of the line would change.
I was working on the codes in ggplot by Hadley Wickham from his article layered grammar of graphics where he demonstrated this feature for drawing Minard's March. I could reproduce most of Minard's March through Gadfly, but the variable thickness of the lines would be useful.

[bjarthur]

have you tried line_width in a Theme? see http://gadflyjl.org/stable/lib/gadfly/#Gadfly.Theme