imports on main __init__

[arsenovic]

importing the sub-packges in the main init would be nice, to be able to do things like

import mpltools
mpltools.style.use('ggplot')

also, distributing with more styles would be nice. the ggplot one is awesome.

[tonysyu]

I'm open to this idea, but I'm not so sure that it's any easier than:

from mpltools import style
style.use('ggplot')

That said, if you submit a PR for it, I'll accept it. As for styles, PRs are certainly welcome, but I don't have any particular styles in mind.