V1.0.1

Add per-point sensor arrays and point feature conversion

- Accumulate gpxtpx track-point extensions into parallel arrays on the
  track Feature (heart_rates, cadences, powers, speeds, temperatures,
  elevations, times)
- Add typed array accessors: gpxHeartRates, gpxCadences, etc.
- Add gpxPointFeatures() to expand MultiLineString into individual
  Point features with per-record sensor data
- Add time-window, distance-window, and fractional-window slicing
  of point features

v1.0.0

Initial release