Bind the given keycode within the contexts to invoke proc. contexts is a list of event-contexts (e.g., '(button1 sidebar)) keycode is an X/11 key code, modifier-mask is the bitmask of modifiers, proc is a procedure that will be invoked (with no arguments) when the specified key is pressed in the specified context. release-proc is a procedure that will be invoked (with no arguments) when the specified key is released in the specified context, or #f or omitted if nothing should be done on key release.