Further work on libdivecomputer integration

Further work on libdivecomputer integration

.. this now registers the dive parsing callback, and starts to parse the
data.  So I can see the last divetime on my Suunto Vyper Air now.

Still a lot more boilerplate stuff to go, though.  The libdivecomputer
interfaces really are pretty insane: why should the caller set up the
dive parsing for each computer type, when libdivecomputer knows what
types it has? IOW, much of that boilerplate should be hidden inside of
libdivecomputer, rather than exposed to the user.

But whatever.  I'm taking pieces from "examples/universal.c" as I go
along (it's under LGPL 2.1).  I want to do it in small chunks just to
feel that I understand what's going on, rather than just blindly copying
it all.

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