Add "native" Suunto SDE zip file reading

You need to have libzip-devel installed, and pkg-config needs to know about it
for the build to pick up on it.

On at least Fedora, a simple "yum install libzip-devel" will make things
work, although you may need to force a rebuild of subsurface too (the
"file.o" file in particular - the Makefile doesn't track system
dependencies).

Then, you can just do

   subsurface my-dives.SDE

to read the data directly from the SDE file.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>