Fixed issues #3, #4, #5

[dylansmith]

• Fixed #3:
  • #rename_dir now takes an itemCallback which is called after each file is processed
• Fixed #4:
  • Improved logging and error handling
  • improved readability of cli output reporter
• Fixed #5:
  • Replaced the EXIF parsing library from exif to
    exif-parser to fix issues with date
    parsing. This does however change the structure of the metadata object used in
    templating (all EXIF tag values now exist within the exif and gps keys only).
• Other improvements:
  • require_exif config option now defaults to false
  • -c cli switch will now also set require_exif to true