Move to PIL for EXIF; add PNG metadata extractor; modularize metadata extraction
Move to PIL for EXIF; add PNG metadata extractor; modularize metadata extraction

Switch back to exifread; PIL's EXIF support sucks.

Dymaxion00/PyCIRCLean,Rafiot/PyCIRCLean,CIRCL/PyCIRCLean,CIRCL/PyCIRCLean,Rafiot/PyCIRCLean