Create static directories at build, not runtime.

Instead of calling lfs.mkdir() to create "./history" and "./screenshots"
at runtime it is easier to create them at package build time.
I hesitated whether to add "./clipboard" to this list but decided
against it as we can perhaps change current directory and then
all the code manipulating clipboard would break, so I left it as is.

Conflicts:

	filechooser.lua
	screen.lua
	settings.lua

Makefile

@@ -220,7 +220,7 @@ customupdate: all
 	$(STRIP) --strip-unneeded kpdfview
 	-rm kindlepdfviewer-$(VERSION).zip
 	rm -Rf $(INSTALL_DIR)
-	mkdir $(INSTALL_DIR)
+	mkdir -p $(INSTALL_DIR)/{history,screenshots}
 	echo $(VERSION) > $(INSTALL_DIR)/git-rev
 	cp -p README.md COPYING kpdfview $(LUA_FILES) $(INSTALL_DIR)
 	mkdir $(INSTALL_DIR)/data