restore 404.html move

Author: Secrus

Makefile

@@ -40,6 +40,7 @@ htmllive: _ensure-sphinx-autobuild html
 .PHONY: dirhtml
 dirhtml: BUILDER = dirhtml
 dirhtml: html
+	mv $(BUILDDIR)/404/index.html $(BUILDDIR)/404.html
 
 ## search         to rebuild the search index
 .PHONY: search