Allow LIBDCDEVEL to specify a path

That's something I had wanted to fix so many times...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Add Ubuntu packaging instructions

These files knowingly (one might say, intentionally) violate the spirit
and letter of the Debian / Ubuntu packaging rules. They are intended to be
able to create our own packages that include their own libdivecomputer,
libgit2 and (later) libmarble. Especially for daily builds this is WAY
easier than fighting with whatever may be the current version of these
packages in Ubuntu (especially since this allows us to use our private
libdivecomputer branch).

This assumes that the user runs the make-package.sh script from a
directory below which we have
subsurface/                <- Subsurface checked out git tree
subsurface/libdivecomputer <- desired libdivecomputer sources
subsurface/libgit2         <- desired libgit2 source

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Allow static libgit2

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Adjust version numbering for Ubuntu package

Let's use all four digits as 'version'.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Make sure Ubuntu package built script is started from the right directory

I kept starting it from within the subsurface directory which of course failed
but left clutter around.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>