The key idea is to pass a continuation function when we call
lean-server-send-cmd function. The passed continuation function is
called by lean-server-event-handler. Until the buffer is ready, the
event handler will be called in interval (lean-server-retry-time, 0.1
sec by default). When we have 'NAY' for INFO command, it will re-send
INFO commands to lean-server until we have one without 'NAY'.
Close#123
If (current-idle-time) is non-zero, we need to set a timer to run
eldoc-documentation-function again when idle-time = (current-idle-time)
+ retry-delay.
