Improves behaviour when send-buffers are filled:

• these packets are no longer considered lost; a sends_blocked field has been added to count the number of occurrences
• if any sends were blocked, the warning message "throughput throttled by buffer limitations" will be added to the summary in non-JSON mode
• messages appear with WARNING-level severity on the sender's side when a send is blocked
  If interacting with a pre-0.1.8 peer, sends_blocked will be set to 0 to allow for interoperability during the upgrade process.

Improves loss-reporting:

• when a UDP receiver observes loss, an INFO-level log-message will be generated on the receiver's side, indicating the size of the gap
  • this is not reflected in the protocol itself, since a lossy connection is likely to have many gaps, and they may be backfilled through out-of-order observation, leading to a very complex structure, but this may be helpful in determining the nature of a network failure when using rperf interactively

Improves end-of-test UDP signaling:

• previously, a burst of five packets were naively emitted at the end of a test; these now respect send-buffers to ensure all five are actually written to the networking stack

UDP jitter is now calculated based on the longest unbroken sequence in each interval, rather than the last.