Release notes for Kaffelogic Nano 7 firmware

Current release version 7.3.9.991 released 5 August 2019

version 7.3.9 - improve error handling of USB Memory Stick - this should eliminate the zero-byte file phenomenon
              - display USB icon when logging starts - this helps assure the user that logging is taking place
              - increase 'debounce' times of buttons to prevent accidental double pushes being detected

version 7.3.8 - implement logging of events: colour change, first crack start/end, second crack start/end, roast end
                user can select one of those events with the - and + buttons when the display shows 'Press > now to log first crack'

version 7.3.7 - fix watchdog timer issue (timeout was 4sec for 4sec process causing rare spurious watchdog alarms)
              - always turn on in ready mode (instead of staying in timer mode if user has put it into timer mode)

version 7.3.6 - 'heat too fast' detection modified to avoid false alarms with unusual profile curves that start out flat for the first few seconds
              - fix small bug in preheat power calculation for profiles that call for a different amount of power from the default 1050W 
                (this will affect some profiles when roasting in an environment below 15 deg or above 25 deg, although the effect is tiny)
              - replace text of 'Supply V is x% of recommended with 'Supply V may be low ...' (reduces confusion between voltage and power)
              - ensure ambient temperature is reset to default during resetting (avoids some obscure minor mis-calculation of power requirements in edge cases)
              - perform some startup tests in a different order to provide better testing during the manufacturing process (no effect on the user)
              
version 7.3.5 - 'heat too slow' detection modified to avoid false alarms
              - improve USB timeout settings to avoid reported memory stick issues
              - skip system and hidden files when loading profiles
              - allow zero-length short names
              - log the calibration data
              - suppress 'calibration reqd' message for Pledge Me machines (updater v 3 and 4)
              - don't reset level when entering calibration mode
              - fix small bug in string handling for version strings (trivial)
              - enhanced error reporting for USB to help debug memory stick problems
              
version 7.3.4 - implement calibration of voltage and fan speed including calibration mode for setting these values
              - fix bug where update message was interfering with restoring default profile