v5.0.0

• HAL: Changed GPS module to get native GPS time (monotonic, no leap second).
  WARNING: The native GPS time is not given in standard NMEA messages, so we
  get it from a proprietary message of the GPS module used on gateway reference
  design, u-blox 7. If you are not using the same GPS module, you may have to
  update the lgw_parse_ubx() function.
• HAL: Added lgw_cnt2gps() and lgw_gps2cnt() functions for SX1301<->GPS time
  conversion.
• HAL: Changed serial port configuration for GPS to properly handle binary
  messages (UBX).
• HAL: Added a lgw_gps_disable() function to restore serial configuration as
  it was before HAL initialization.
• HAL: Fixed packet time on air calculation using the actual packet preamble
  size.
• HAL: Adjusted TX_START_DELAY based on the board reference design to ensure
  that a packet is sent exactly at 1500µs after the TX trigger (TIMESTAMP or PPS),
  with a tolerance of +/- 1µs. This is mandatory to comply with LoRaWAN
  specification for Class-B beaconing precise timing.
  WARNING: This release provides tx start delay values to be used for Semtech
  reference designs AP1 and AP2. The HAL automatically detects the board version
  by detecting a FPGA or not. If you are using a different reference design or
  a different FPGA binary version than the one provided with this release, the
  value to be used for TX start delay may be different.