Move-assign a basic_waitable_timer
from another.
basic_waitable_timer & operator=( basic_waitable_timer && other);
This assignment operator moves a timer from one object to another.
The other basic_waitable_timer
object
from which the move will occur.
Following the move, the moved-from object is in the same state as if constructed
using the basic_waitable_timer(io_service&) constructor
.