Restore left-aligned columns in HTML tables

Override new centered alignment default started in sphinx 2.0.

Author: pavoljuhas

Diff for: _static/diffpy-styles.css

@@ -0,0 +1,5 @@
+/* Restore left-aligned table columns for sphinx 2.0 and later */
+
+table.align-default {
+    text-align: left;
+}

Diff for: conf.py

@@ -361,4 +361,5 @@ def apply(self):
 
 def setup(app):
     app.add_transform(MakeAbsoluteURIsRelative)
+    app.add_css_file('diffpy-styles.css')
     return