https://bugzilla.gnome.org/show_bug.cgi?id=791121

gi now emits a warning when not loading a specific library
version [1]:

  ./generate-setting-docs.py:21: PyGIWarning: NM was imported without specifying a version first. Use gi.require_version(NM, 1.0) before import to ensure that the right version gets loaded.
    from gi.repository import NM, GObject

Seems require_version() is reasonably old to just always use it without
breaking on older versions [2].

[1] Related: https://bugzilla.gnome.org/show_bug.cgi?id=727379
[2] https://git.gnome.org/browse/pygobject/commit/?id=76758efb6579752237a0dc4d56cf9518de6c6e55

Remove _nm_object_ensure_inited(), etc; objects that implement
GInitable are now mandatory-to-init().

Remove constructor() implementations that sometimes return NULL; do
all the relevant checking in init() instead.

Make nm_client_new() and nm_remote_settings_new() take a GCancellable
and a GError**.

Since the API has not changed at this point, this is mostly just a
matter of updating Makefiles, and changing references to the library
name in comments.

NetworkManager cannot link to libnm due to the duplicated type/symbol
names. So it links to libnm-core.la directly, which means that
NetworkManager gets a separate copy of that code from libnm.so.
Everything else links to libnm.

jklimes:
made the change for new firewall-zone.py example as well.

Move examples using dbus-python ('dbus' module) and GObject introspection into
their own directories.