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.