v4.0.0

• drop support of electronic hardware v1 and v2
  (from now on, minimum compatibility is from v3)
• refactor main loop and breathing control
  (breathing-related computations are now triggered by a hardware timer)
• support several breathing modes
  (PC-CMV stays the default mode, PC-VSAI and PC-AC were added)
• added volume controlled ventilation modes
  (VC-CMV and VC-AC were added)
• telemetry protocol v2 was introduced
  (basically, this means sending more data)
• drop support of useless "qualification" and "integration test" modes
  (both are superseded by the EOL test feature)
• add a watchdog for the Raspberry Pi
  (RPi power supply will be restarted if UI misses sending heartbeats)
• allow to set any setting (current or added) using the serial control protocol
  (new settings were added, and they can all be changed from UI software)
• improve breathing control algorithms
• remove ability to set peak pressure
• allow to snooze alarms or start/stop breathing using the serial control protocol
• drop support of old valves and pneumatic systems
• make mass flow meter more reliable
• support for SFM mass flow meters
  (SFM3019 and SFM_3300D)
• added support for a mass flow meter on the expiratory branch
  (if it is missing, the expiratory flow rate will be estimated using an algorithm)
• turn the green LED on when alarms are snoozed
• added a facility to pre-configure the ventilator settings upon boot, using a patient height setting
  (submitting the patient height will update all ventilation hyperparameters to optimum values)
• added configurable alarms for pressure and volume modes, adding to all existing alarms
• sending more measured values for display, e.g. respiratory durations and cycles per minute
• a more precise battery voltage value is now sent over the telemetry protocol
  (this is used for battery SoC estimations)
• display a special message on LCD screen when watchdog reset was triggered
• ability to detect in a reliable way when AC gets off, and that power is switched to battery
• allow to retry pressure calibration when it fails
• added a ramp-up algorithm on the blower speed controller, in order to prevent current surges in the transformer, which could trigger a temporary handover on batteries
  (this is a security feature, in cases where batteries would be depleted or not connected, the ventilator would suddenly reboot during use)
• added a compilation flag to disable all hardware buttons
  (this is used for touchscreen-only MakAir devices, i.e. non-traditional ones)
• added basic support for the motherboard V3 EEPROM chip over I2C
  (disabled by default until stable)
• a lot of potential exceptions due to possible divisions by zero have been fixed
• increase the size of the hardware buffer used by telemetry
• improve Doxygen documentation