Runtime/bespoke format support like kaitai struct

Not a bug report, but a suggestion that might make supporting any format useful (I tend to work with really weird bespoke binary formats).

Any thoughts on adding support for arbitrary format support. Something like "if the decoded format isn't found, then try to resolve it as a file and load that".

i.e. fq --decode zxtap.go ".headers" game.tap - where zxtap.go follows your format file convention. Then I could make my own formats without having to rely on native support inside of fq (also solves those requests asking for other formats that have been raised already).