3.23.1: 2021-09-21
  Improve ubx cycle detection.
  Add quirks for Jackson Labs nonstandard NMEA
  Change STATUS_NO_FIX to STATUS_UNK to avoid confusion with fix mode.
  Change STATUS_FIX to STATUS_GPS to avoid confusion with fix mode.
  Change STATUS_DGPS_FIX to STATUS_DGPS to avoid confusion with fix mode.
  Split SOURCE_ACM from SOURCE_USB.  ACM has no speeds.
  Add speeds 1 mbps, 1.152 mbps, 1.5 mbps, and higher.  When libc supports them.
  Improve autobaud.
  Add new u-blox M10 messages.
  Fix u-blox M6, M7 initialization issues.
  Various ubxtool and gpxlogger updates.
  Add mtk3301_speed_switcher()
  No API changes, except for STATUS_* as above.
  No ABI changes.
  Fallback to "python3" if "python" not found.

Signed-off-by: Nick Hainke <vincent@systemli.org>