docs: reorganize tcg-plugins.rst

Clean up the heading levels to use === --- ~~~, and create a new "writing
plugins" section.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/devel/tcg-plugins.rst

@@ -3,7 +3,6 @@
    Copyright (c) 2019, Linaro Limited
    Written by Emilio Cota and Alex Bennée
 
-================
 QEMU TCG Plugins
 ================
 
@@ -16,8 +15,30 @@ only monitor it passively. However they can do this down to an
 individual instruction granularity including potentially subscribing
 to all load and store operations.
 
-API Stability
-=============
+Usage
+-----
+
+Any QEMU binary with TCG support has plugins enabled by default.
+Earlier releases needed to be explicitly enabled with::
+
+  configure --enable-plugins
+
+Once built a program can be run with multiple plugins loaded each with
+their own arguments::
+
+  $QEMU $OTHER_QEMU_ARGS \
+      -plugin tests/plugin/libhowvec.so,inline=on,count=hint \
+      -plugin tests/plugin/libhotblocks.so
+
+Arguments are plugin specific and can be used to modify their
+behaviour. In this case the howvec plugin is being asked to use inline
+ops to count and break down the hint instructions by type.
+
+Writing plugins
+---------------
+
+API versioning
+~~~~~~~~~~~~~~
 
 This is a new feature for QEMU and it does allow people to develop
 out-of-tree plugins that can be dynamically linked into a running QEMU
@@ -25,9 +46,6 @@ process. However the project reserves the right to change or break the
 API should it need to do so. The best way to avoid this is to submit
 your plugin upstream so they can be updated if/when the API changes.
 
-API versioning
---------------
-
 All plugins need to declare a symbol which exports the plugin API
 version they were built against. This can be done simply by::
 
@@ -43,18 +61,8 @@ current API versions supported by QEMU. The API version will be
 incremented if new APIs are added. The minimum API version will be
 incremented if existing APIs are changed or removed.
 
-Exposure of QEMU internals
---------------------------
-
-The plugin architecture actively avoids leaking implementation details
-about how QEMU's translation works to the plugins. While there are
-conceptions such as translation time and translation blocks the
-details are opaque to plugins. The plugin is able to query select
-details of instructions and system configuration only through the
-exported *qemu_plugin* functions.
-
-Query Handle Lifetime
----------------------
+Lifetime of the query handle
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Each callback provides an opaque anonymous information handle which
 can usually be further queried to find out information about a
@@ -63,32 +71,8 @@ valid during the lifetime of the callback so it is important that any
 information that is needed is extracted during the callback and saved
 by the plugin.
 
-API
-===
-
-.. kernel-doc:: include/qemu/qemu-plugin.h
-
-Usage
-=====
-
-Any QEMU binary with TCG support has plugins enabled by default.
-Earlier releases needed to be explicitly enabled with::
-
-  configure --enable-plugins
-
-Once built a program can be run with multiple plugins loaded each with
-their own arguments::
-
-  $QEMU $OTHER_QEMU_ARGS \
-      -plugin tests/plugin/libhowvec.so,inline=on,count=hint \
-      -plugin tests/plugin/libhotblocks.so
-
-Arguments are plugin specific and can be used to modify their
-behaviour. In this case the howvec plugin is being asked to use inline
-ops to count and break down the hint instructions by type.
-
-Plugin Life cycle
-=================
+Plugin life cycle
+~~~~~~~~~~~~~~~~~
 
 First the plugin is loaded and the public qemu_plugin_install function
 is called. The plugin will then register callbacks for various plugin
@@ -111,11 +95,26 @@ callback which can then ensure atomicity itself.
 Finally when QEMU exits all the registered *atexit* callbacks are
 invoked.
 
+Exposure of QEMU internals
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The plugin architecture actively avoids leaking implementation details
+about how QEMU's translation works to the plugins. While there are
+conceptions such as translation time and translation blocks the
+details are opaque to plugins. The plugin is able to query select
+details of instructions and system configuration only through the
+exported *qemu_plugin* functions.
+
+API
+~~~
+
+.. kernel-doc:: include/qemu/qemu-plugin.h
+
 Internals
-=========
+---------
 
 Locking
--------
+~~~~~~~
 
 We have to ensure we cannot deadlock, particularly under MTTCG. For
 this we acquire a lock when called from plugin code. We also keep the
@@ -142,7 +141,7 @@ requested. The plugin isn't completely uninstalled until the safe work
 has executed while all vCPUs are quiescent.
 
 Example Plugins
-===============
+---------------
 
 There are a number of plugins included with QEMU and you are
 encouraged to contribute your own plugins plugins upstream. There is a