Symlink directory traversal security fix

Fixed dirtraversal test; updated extractor to not fork unless necessary (nose tests don't like sys.exit)

Removed hilink decryption plugin; contains priprietary crypto key(s).

530 fix sasquatch in binwalk docker container

Ubuntu Focal is Python 3 by default

https://wiki.ubuntu.com/FocalFossa/ReleaseNotes#Python3_by_default
Several other distros as well.

Fix: binwalk stuck when extract encrypt zip files

Call 'unzip' with empty password, to avoid 'unzip' stuck in interactive mode when process encrypt files

525 publish binwalk as a docker image

Actually implement exponent and shift operators