Add support for squashfs

[ci-macpaw]

Originally reported on Google Code with ID 667

megaminxwin:

This is a compressed filesystem that seems to be getting more popular, and it would
be nice if it was implemented since I'm beginning to see a few files around that use
it.

[ci-macpaw]

paracelsus:

It looks like there are four different versions of the format. Implementing it from
scratch would probably be too much work to be worth it.

The source looks like it could be re-used, but it is licensed under the GPL, so it
is incompatible with the LGPL The Unarchiver uses.

If anyone could convince the author to relicense it, it would be possible, though.

[ci-macpaw]

megaminxwin:

Here's the original home page for it: http://squashfs.sourceforge.net/

I don't know how useful that would be, but it's all I could find.

[ci-macpaw]

paracelsus:

That sounds like a reasonable idea. Feel free to post links to information or source
code related to it, to get things started.