ntpstats 3.4.0

GNSS timing receivers and time-stamping sources. No breaking changes.

Added

• u-blox UBX receiver logs (format ubx, detected automatically, also mixed with NMEA and in the
  web UI): UBX-NAV-CLOCK becomes a receiver-clock series (bias as reported, with drift, time and
  frequency accuracy), UBX-NAV-TIMEUTC time-stamps it, and UBX-TIM-TP gives the time-pulse
  quantization error qErr. Layouts from the u-blox interface description. (#21)
• ntpstats sawtooth and ntpstats.ubx.apply_qerr: remove the PPS quantization sawtooth from a
  time-interval-counter measurement with the receiver's qErr. The sign with which qErr applies
  (not stated by u-blox) is chosen from the data and reported, or given with --sign; TDEV before
  and after is printed.
• chrony time-stamping sources: measurements.log series carry interleaved, tx_timestamp and
  rx_timestamp (daemon, kernel or hardware) and a summary in meta["timestamping"], also shown on
  the web UI's network page.
• Gallery notebook Removing the GNSS PPS sawtooth with u-blox qErr, with a synthetic receiver log
  and counter log (examples/data/ubx-timing.ubx, pps-tic.csv). (#38)

Changed

• Times below a femtosecond are printed as 0 (they are numerical noise).

Stable API changes since 3.3.0

• None. Code written against the stable API of an earlier release keeps working.