docs/interop: Convert qmp-spec.txt to rST

Convert the qmp-spec.txt document to restructuredText.
Notable points about the conversion:
 * numbers at the start of section headings are removed, to match
   the style of the rest of the manual
 * cross-references to other sections or documents are hyperlinked
 * various formatting tweaks (notably the examples, which need the
   -> and <- prefixed so the QMP code-block lexer will accept them)
 * English prose fixed in a few places

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230515162245.3964307-2-peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
[.. code-block:: dumbed down to :: to work around CI failure]

qapi/control.json

@@ -27,7 +27,7 @@
 # Notes: This command is valid exactly when first connecting: it must
 #     be issued before any other command will be accepted, and will
 #     fail once the monitor is accepting other commands.  (see qemu
-#     docs/interop/qmp-spec.txt)
+#     docs/interop/qmp-spec.rst)
 #
 #     The QMP client needs to explicitly enable QMP capabilities,
 #     otherwise all the QMP capabilities will be turned off by
@@ -46,7 +46,7 @@
 # connection, used for agreeing on particular QMP extension behaviors.
 #
 # @oob: QMP ability to support out-of-band requests.  (Please refer to
-#     qmp-spec.txt for more information on OOB)
+#     qmp-spec.rst for more information on OOB)
 #
 # Since: 2.12
 ##

qapi/qapi-schema.json

@@ -29,7 +29,8 @@
 #   -> data issued by the Client
 #   <- Server data response
 #
-# Please, refer to the QMP specification (docs/interop/qmp-spec.txt)
+# Please refer to the
+# :doc:`QEMU Machine Protocol Specification </interop/qmp-spec>`
 # for detailed information on the Server command and response formats.
 ##