Correct documentation configuration (#1684)

There is an internal link to 'specifications' that requires a Sphinx extension to be installed to work.

There are no  custom static files, so removed spurious mention to `_static` directory,

docs/source/conf.py

@@ -25,7 +25,7 @@
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = []
+extensions = ['sphinx.ext.autosectionlabel']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -123,7 +123,7 @@
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+# html_static_path = ['_static']
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.