Add the capability to print a dive profile

Add the capability to print a dive profile

Ok, this is the ugliest f*&$ing printout I have ever seen in my life,
but think of it as a "the concept of printing works" commit, and you'll
be able to hold your lunch down and not gouge out your eyeballs with a
spoon.  Maybe.

I'm just doing the cairo display as-is for the printout, which is a
seriously bad idea.  I need to not try to do colors etc, and instead of
having white lines on a black background I just need to make thelines be
black on white paper.

But that would involve actually changing the current "plot()" routine,
which is against the point of the exercise right now.  This really is
just a demonstration of how to add printing capabilities.

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