Just do a mk and run the resulting binary.  Rio works as normal,
except that mid-clicking outside of any window brings up a menu with
the different virtual desktops listed.

To my knowledge, this works just like p9p rio's virtual desktops.

The new options:

'-n' will enable "nostalgia mode", which for now emulates the 8½
window border color and style.

'-b 0xrrggbbFF' will set the background color to rrggbb.  The trailing
'FF' does not appear to be important.  The default color is
0x777777FF.