Fix how images are converted to PIL

Can now support float32, float64, bool and uint8 images. uint8
images are untouched, the rest are converted and scaled by 255.

Floating point images outside of the range of [0, 1] throw an
exception now
Stop printing so many 's's!

Thanks @trigeorgis!
Merge pull request #516 from patricksnape/as_pil

Fix how images are converted to PIL