gm.tsl make a line plot in time serie format.
Graphic models function family make graphic creation easy, is recommended for new programers,
they have less and easyful parameters then p.tsl but the graphic customize is more limited.
The data don't need be a ts object.
# NOT RUN {v=data.frame("x"=seq.Date(as.Date('2020-01-01'),
to = as.Date('2020-04-01'),by='month'),"y"=c(5,3,7,2))
gm.tsl(v,1,2,title="Simple example",ntimes=3)
# }