client: improve FLOOD_WAIT handling

[ernado]

Currently in most cases FLOOD_WAIT handling is user responsibility. However, it is not convenient.

We can implement some sort of invoker wrapper:

1. Separate flood-waits per request/scope?
2. Automatic retries (at least one time)?
3. Way to provide user a signal about flood_wait

This is pretty hard to get right, because ideally there should be some kind of queue of requests (say scheduler).

[ernado]

Related: #271

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.