Allow EXIF data to have commas in the value

Except for a handful of fields known to encode their data in a
comma-separated list of character values -- ExifVersion and
FlashPixVersion. This allows other values, like GPSLongitude,
GPSLongitude, BitsPerSample, etc... to be extracted with incorrectly
"decoding" them. It fixes #36, where GPS info often caused EXIF data
extraction to break due to the numbers not being valid character codes.
Merge pull request #271 from stevenharman/allow_commas_in_general_exif_data

Allow EXIF data to have commas in the value