Subscriber backlog tool

[QIvan]

Regard to discussion in #482 I wrote my understanding how streamStats work down to the code.
Output of this tool looks like:

sessionId=508185878 streamId=10 channel=aeron:udp?endpoint=localhost:40123 : 
┌─for publisher 5 the last known position is 60069504 (~8416768 bytes before a back-pressure)
└─sender 5 is up to position 60097856 (103872 bytes the sender may send up to ASAP.)
┌─receiver 7 is up to position 60097664
└─subscriber 2 has 0 bytes in backlog

sessionId=508185877 streamId=10 channel=aeron:udp?endpoint=localhost:40124 : 
┌─for publisher 4 the last known position is 60069568 (~8416704 bytes before a back-pressure)
└─sender 4 is up to position 60097856 (101888 bytes the sender may send up to ASAP.)
┌─receiver 6 is up to position 60097664
└─subscriber 3 has 0 bytes in backlog

[mjpt777]

Thanks @QIvan this is nice work.

[QIvan]

wow! Seems like today is my personal holyday ;-)
Thank you very much!