Subscribe for events from a given block

[khssnv]

Allow events listening from a given (historical or future) block. Best block events will are on hold until the historical events sequentially processed. Default queue size is 20 000 blocks (source) which with 6 seconds block time gives us about 33 hours to process historical events before overflow. Also events listeners invocation made synchronous and a client may provide a callback function to call after all events listeners are done with a certain block events.