Implement more magic

[shawngmc]

Right now, the file identification code relies heavily on libmagic. While the libmagic integration is a little fragile, that can be improved separately.

The bigger concern is that the 'enhanced magic' is very limited:

• Only a few types detected
• All are hard-coded into the script

As such, the following improvements make sense

• Move the custom magic to an JSON-based format
• Add more magic detections
  • What's the process for adding to libmagic?
  • Also pull from/add to the Wikipedia: List of file signatures