What's actually needed here is an explaination of how the license
applies along with the explanation where to find the full text.

Also, the libnm documentation was lacking the licensing information
altogether. Fix fixes it too.

gtkdoc-scan supports regular expressions in the --ignore-decorators
command-line option. Since it is easier to use a regexp than grepping
macros from a source file, revert the ugly solution from commit
2d941dc95a1d ('build: fix errors when building with gtk-doc 1.32').

gtkdoc-scan 1.32 performs stricter checks on structures definitions
and so it complains on:

 /build/networkmanager/src/NetworkManager/libnm/./nm-vpn-plugin-old.h:0: warning: partial declaration (struct) : typedef struct {
 	NM_DEPRECATED_IN_1_2
 	GObject parent;
 } NMVpnPluginOld NM_DEPRECATED_IN_1_2;

because of the unrecognized token 'NM_DEPRECATED_IN_1_2'.

Pass all allowed macros to gtkdoc-scan through the --ignore-decorators
argument.

https://gitlab.gnome.org/GNOME/gtk-doc/issues/98
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/238

For now only add the core settings, no peers' data.

To support peers and the allowed-ips of the peers is more complicated
and will be done later. It's more complicated because these are nested
lists (allowed-ips) inside a list (peers). That is quite unusual and to
conveniently support that in D-Bus API, in keyfile format, in libnm,
and nmcli, is a effort.
Also, it's further complicated by the fact that each peer has a secret (the
preshared-key). Thus we probably need secret flags for each peer, which
is a novelty as well (until now we require a fixed set of secrets per
profile that is well known).

We named the types inconsistently:

  - "p2p-wireless" ("libnm-core/nm-setting-p2p-wireless.h")

  - "p2p" ("libnm/nm-p2p-peer.h")

  - "p2p-wifi" ("src/devices/wifi/nm-device-p2p-wifi.h")

It seems to me, "libnm/nm-p2p-peer.h" should be qualified with a "Wi-Fi"
specific name. It's not just peer-to-peer, it's Wi-Fi P2P.
Yes, there is an inconsistency now, because there is already
"libnm/nm-access-point.h".

It seems to me (from looking at the internet), that the name "Wi-Fi P2P"
is more common than "P2P Wi-Fi" -- although both are used. There is also
the name "Wi-Fi Direct". But it's not clear which name should be
preferred here, so stick to "Wi-Fi P2P".

In this first commit only rename the files. The following commit will
rename the content.

This adds the introspection data and P2P peer handling to libnm. To be
usable the P2P device handling is also needed.

The support is rather basic and only allows connecting to a specific
peer. However, this is actually already enough for many usecases.

Add missing trailing commas that avoids getting noise when another
file/parameter is added and eases reviewing changes[0].

[0] https://gitlab.gnome.org/GNOME/dconf/merge_requests/11#note_291585