Offline backlog uploads in full after reconnecting: Signal K AIS plugin 0.3.1

Fixes a queue that never emptied. While the plugin was replaying a backlog to aiscast it wrote every sentence its receiver heard to a new queue file, so it traded one file for another and the replay never reached the end. On a boat that had been offline a while, the queue directory stayed at tens of thousands of files no matter how long the connection was up. A replay now carries up to a thousand sentences from as many files in one frame, and sentences heard mid-replay go out from memory.
The queue keeps far fewer files. Time offline used to leave one behind every fifteen seconds; the plugin now fills each file to 500 sentences before starting another, so the count follows how much is owed rather than how long the boat was out of range.
Sentences past the server's publish limit are no longer lost. aiscast accepts 6000 sentences a minute and quietly drops the rest, so a large replay used to arrive mostly empty while the plugin counted it as delivered. The plugin now paces a replay under the limit and keeps anything the server did not take. A boat with a big backlog takes about a minute for every 5400 sentences owed to catch up, with live sending held back until it is done.