`sphinx.ext.graphviz`: show graph image in inline by default

To support subsutituion syntax, make graphviz node inline (ref: #1149).
Now graphviz directive behaves like ``image`` directive when no captions.
If specified, it generates ``figure`` node and ``caption`` node like
``figure`` directive.

tests/roots/test-ext-graphviz/conf.py

@@ -2,4 +2,12 @@
 
 extensions = ['sphinx.ext.graphviz']
 master_doc = 'index'
+<<<<<<< 492f60c37185dccee1e42c01fb5d87ed42f45608
 exclude_patterns = ['_build']
+=======
+
+latex_documents = [
+    (master_doc, 'SphinxTests.tex', 'Sphinx Tests Documentation',
+     'Georg Brandl', 'manual'),
+]
+>>>>>>> ``sphinx.ext.graphviz``: show graph image in inline by default

tests/roots/test-ext-graphviz/index.rst

@@ -5,3 +5,9 @@ graphviz
    :caption: caption of graph
 
    bar -> baz
+
+.. |graph| digraph:: bar
+
+           bar -> baz
+
+Hello |graph| graphviz world