bellwood

This release stabilizes the programmable filters, making it possible to manipulate telemetry and logs in-flight with user-written lua code. This is a big accomplishment, one of the long-term goals of cernan is now achieved.

This release also fixes a bug in the interpretation of gauges by making a hard distinction between delta-gauges and gauges. Previously their individual behaviours were somewhat confused.

Lastly, this release introduces some performance improvements driven by callgrind profiling of cernan. There's more that can be done--especially around metrics which are mostly the same internally--but this was all low-hanging fruit.