doc: Formalize file comment in wayland-client.h, wayland-server.h

Publican was generating a subtle error during a build:
Error: no ID for constraint linkend: Server-wayland-server-core_8h.

This was caused by doxygen applying the doc comment at the top of
wayland-server.h as the documentation for struct wl_object. As such, the
generated documentation for wl_object was also very incorrect.

Make the file doc comments in wayland-client.h and wayland-server.h real
doxygen file doc comments with the \file command, add a \brief, make the
inclusion warning a \warning, correct the language of the comment in
wayland-server.h, and remove one unnecessary line break.

This squelches the publican error, removes the bad wl_object documentation,
and makes the comment appear in the generated html documentation.

References: d74a9c079b

Signed-off-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>

src/wayland-client.h

@@ -23,8 +23,11 @@
  * SOFTWARE.
  */
 
-
-/** Use of this header file is discouraged. Prefer including
+/** \file
+ *
+ *  \brief Include the client API and protocol C API.
+ *
+ *  \warning Use of this header file is discouraged. Prefer including
  *  wayland-client-core.h instead, which does not include the
  *  client protocol header and as such only defines the library
  *  API.

src/wayland-server.h

@@ -23,10 +23,13 @@
  * SOFTWARE.
  */
 
-
-/** Use of this header file is discouraged. Prefer including
+/** \file
+ *
+ *  \brief Include the server API, deprecations and protocol C API.
+ *
+ *  \warning Use of this header file is discouraged. Prefer including
  *  wayland-server-core.h instead, which does not include the
- *  client protocol header and as such only defines the library
+ *  server protocol header and as such only defines the library
  *  API, excluding the deprecated API below.
  */