DOC: image tutorial touch-up

- expand some text regarding backend usage and IPython notebook plot
- improve style a bit (PEP 8)
- shorten array printout
- convert image resizing example to use PIL
- replace pyplot discussion in top material
- remove matplotlib argument to IPython in intro
Merge remote-tracking branch 'msarahan/ImageTutorialNotebookEdit'

Conflicts:
	doc/users/image_tutorial.rst