Add support for KGB format

[ci-macpaw]

ThePezman (ThePezman):

Originally reported on Google Code with ID 327

ThePezman:

http://kgbarchiver.net/?page=download
http://filext.com/file-extension/kgb
http://en.wikipedia.org/wiki/KGB_Archiver

This appears to be an esoteric compression format, so I'm not sure if it would be worth
it, but I have found a file or two compressed in this format.

[ci-macpaw]

paracelsus:

Apparently KGB is based in PAQ6, which is GPL, and thus incompatible with the The Unarchiver
license (LGPL). Adding support would either require re-implementing from scratch (unlikely
to ever happen), or the author of PAQ changing the license to LGPL.

[ci-macpaw]

paracelsus:

Hmm, at least there appears to be source code.

Not going to add this quite yet, probably, but if someone would find support useful,
please speak up in here.