Add support for reading file magic from FFW

[anjackson]

The FFW supports documenting format magic numbers, tagged as {{magic}}. Can this be added to the extractor code so it appears in the aggregator?

[thorsted]

Sometimes the magic tags are in the body and other times in the header of the wiki article. They also vary from hex bytes to ascii. If there is a preferred method, I can suggest conformance.

Examples:
http://fileformats.archiveteam.org/wiki/RCA-VOC
http://fileformats.archiveteam.org/wiki/PSF_(PhotoStudio)