async: add client-object proxy

Add a class which acts as a client-side proxy to a object.  The
proxy holds the object address (service, path, interface) and
creates Senders for standard dbus operations: method-call,
get-property, set-property, get-all-properties.  These Senders
can also be used in co-routine contexts (via co_await).

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4b2e50a8b55d10975984ac4244bb075db8746fbf
diff --git a/example/meson.build b/example/meson.build
index 17fd569..1850596 100644
--- a/example/meson.build
+++ b/example/meson.build
@@ -33,6 +33,12 @@
 )
 
 executable(
+    'coroutine-example',
+    'coroutine-example.cpp',
+    dependencies: [ sdbusplus_dep ],
+)
+
+executable(
     'register-property',
     'register-property.cpp',
     dependencies: asio_dep,