adding ability to import and export PIL image objects from memory

Hi, I'm a first-time contributor to scikit-image. Me and my team ran into a problem yesterday - we want to import and export PIL images into scikit-image without reading or writing from disk. The current version of pil_plugin.py doesn't have APIs for this. I refactored the plugin a bit to add APIs for importing and exporting PIL images directly. Here's the pull request: https://github.com/scikit-image/scikit-image/pull/1083 I'm not sure who to ask - but will someone review this pull request and let me know if there are problems with it? Or if it could be improved? cheers adam -- Adam Feuer Seattle, WA, USA