Add doctest ext

Author: Julian

docs/conf.py

@@ -25,7 +25,12 @@
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = ['sphinx.ext.ifconfig', 'sphinx.ext.todo', 'sphinx.ext.intersphinx']
+extensions = [
+    'sphinx.ext.ifconfig',
+    'sphinx.ext.todo',
+    'sphinx.ext.intersphinx',
+    'sphinx.ext.doctest',
+]
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']