Disable unused, obsolete sphinx extension pngmath.

Also comment out non-existent directory for static sphinx files.

Author: pavoljuhas

doc/manual/source/conf.py

@@ -32,7 +32,7 @@
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.autodoc', 'sphinx.ext.doctest',
-        'sphinx.ext.coverage', 'sphinx.ext.pngmath', 'sphinx.ext.napoleon']
+              'sphinx.ext.coverage', 'sphinx.ext.napoleon']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -138,7 +138,7 @@
 # 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.