include logx for df.plot()

[zachcp]

I often use scatterplots to show data and if these data are over a range of values it is useful to have a log-log scale. Right now the default df.plot() function supports a logy=True argument but not a logx=True.

I think a logx argument in the plotting function would be a useful addition.

[lodagro]

Usefull indeed.
Easy to work around.

ax = df.plot(logy=True)
ax.set_xscale('log')