Add versioned NM_DEPRECATED_IN_* and NM_AVAILABLE_IN_* macros, and tag
new/deprecated functions accordingly. (All currently-deprecated
functions are assumed to have been deprecated in 0.9.10.)

Add NM_VERSION_MIN_REQUIRED and NM_VERSION_MAX_ALLOWED macros which
can be set to determine which versions will cause warnings.

With the current settings, external consumers of the
libnm-util/libnm-glib APIs will have MIN_REQUIRED and MAX_ALLOWED both
set to NM_VERSION_0_9_8 by default, meaning they will get warnings
about functions added in 0.9.10. NM internally sets
NM_VERSION_MAX_ALLOWED to NM_VERSION_NEXT_STABLE to ensure that it is
always allowed to use all APIs.

Unfortunately, $(AM_CPPFLAGS) gets overridden by per-target _CPPFLAGS
variables, which $(INCLUDES) did not, so this requires some additional
changes.

In most places, I have just gotten rid of the per-target _CPPFLAGS
variables; in directories with a single target, the per-target
variable is unnecessary, and in directories with multiple targets, the
per-target variable is often undesirable, since it forces some files
to be compiled twice, even though there ends up being no difference
between the two files.

This functionality is (mostly) obsoleted by the newer
GLIB_VERSION_MIN_REQUIRED and GLIB_VERSION_MAX_ALLOWED defines.  With
this, your build doesn't all of a sudden blow up if we deprecate
something in GLib - you have to explicitly opt-in to the newer
version.

G_DISABLE_DEPRECATED does still apply for macros and things that can't
take __attribute__((deprecated)), but it's not really worth the pain
and cargo culting around just for that.

nm-version.h is in ${top_builddir}/include.

That allows sharing the code between devices and active connections.

Nothing in cli uses the marshalller stuff.

nmcli uses its own code to dump connections' details instead of
libnm-util's nm_connection_dump(). It allows to structure output
and present values of the settings according to nmcli needs.