Support depacking of 20to4 windows packer

[glennlunder]

A demoscene-oriented executable packer for Windows developed by demoscener muhmac, somewhat popular in the early to mid-2000's. Doesn't appear as if full source is available on GitHub nor anywhere else, so would probably require reverse engineering the code, or contacting muhac directly.

Homepage: http://20to4.net/

Muhmac on Demozoo: http://demozoo.org/sceners/6154/
Muhmac on Pouët: http://www.pouet.net/user.php?who=296

Demozoo tag for productions packed with this packer; http://demozoo.org/productions/tagged/20to4/

[emoon]

Looked at this a bit and likely fairly easy to implement on Windows as it uses standard CAB (which windows has built-in compression for which allow executables not to have their own decompression code) Doing a quick search there seems to be some Linux tools for it also so one can likely look at some code and either rewrite it or use it directly.