timer-based sampling of statistics

Let maestro-core report heartbeat of statistics at a user-defined frequency.

  • Add env variable MSTRO_TELEMETRY_HEARTBEAT in seconds (supporting fractional value). 0 indicates 'disable', and is the default
  • Add thread with sigitimer and lots of sleep (using poll(NULL,...) or sleep or by hooking into a PC thread active timer counting.
Edited by Utz-Uwe Haus