v0.0.13

- compatibility update for XOWA 0.8.1 : XOWA command protocol renaming
xowa: --> xowa-cmd: (for wrking properly e.g. Search box)
- added extensions.xowa_viewer.xowa-cmd_enable preference for disabling
by default xowa-cmd: protocol (I may be not necessery now as there is
pointed in [[Help:XOWA_viewer]] about unimplemented xowa-cmd but I have
implemented this pref before)