Add support for Deflate64 files

[abbeycode]

Issue #37 added a specific message declaring incompatibility when a Deflate64 file is encountered in an archive, but that's really only a stopgap measure. It would obviously be better to actually unzip Deflate64 files. 7-Zip currently does this, and seems to be the only open source software that does.

Look into making use of their code in some way, since it seems that zlib won't ever support Deflate64.

[amosavian]

As I know Deflate64 is protected by patents, thats why you can't find any open source implementation. By the way it also means we should have a kill switch to disable this feature in case it is necessary.