Remove no longer needed generated files in doc

If we use the Google Custom Search API, we do not need to keep the
generated searchindex.js file anymore. We also can safely remove
the _sources directory for good.

Since these get generated during each Sphinx build, additional
steps have been added to the Makefile to get rid of them. They
are also added to .gitignore to avoid commiting them by accident.

doc/Makefile

@@ -42,7 +42,9 @@ html: $(OBJECTS)
 		cp -r src/* $(RSTDIR)/ ;\
 		sphinx-build -j 8 -b html -c utils/sphinx-config -d $(BUILDDIR)/doctrees $(RSTDIR) html ;\
 		deactivate ;\
-	)	
+	)
+	-rm html/searchindex.js
+	-rm -rf html/_sources
 	@echo "Build finished. The HTML pages are in doc/html."
 
 pdf: utils/txt2html/txt2html.exe

doc/html/.gitignore

@@ -1,2 +1,4 @@
 .buildinfo
 objects.inv
+searchindex.js
+_sources