Add a Cretonne domain for Sphinx.

Include roles for documenting IL instructions and types, including
index cross references.

cranelift/docs/conf.py

@@ -19,7 +19,7 @@ import shlex
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+sys.path.insert(0, os.path.abspath('.'))
 
 # -- General configuration ------------------------------------------------
 
@@ -34,6 +34,7 @@ extensions = [
     'sphinx.ext.todo',
     'sphinx.ext.mathjax',
     'sphinx.ext.ifconfig',
+    'cton_domain'
 ]
 
 # Add any paths that contain templates here, relative to this directory.