parameterize beep() to use different sounds for start/stop and interval alarms

added time/temp spreadsheet to repo, trimmed todos

audible alert on start/stop, simplify beep sound

add support for piezo buzzer beeps

configure temp probe handling to use /opt/devtimer/temp_probe symlink

further cleanup and tuning of footswitch debounce logic

tune footswitch debounce logic

implement foot switch handling as an isr with rudimentary debounce logic

update todo

canonicalize references to wiringpi methods and constants

enable basic footswitch control

update todos

initialize the time display on boot

remove unneeded globals file from repo, update todos

cleanup out of range temperature handling

fix leading zero suppression logic, generally tidy up temperature reporting

give time and temp led device objects more descriptive names

update todos

update todos

suppress leading zeros in temp display, add startup temp sentinel, reorg constants and globals

collapse temperature code and globals into main module, implement temp out-of-range signaling

add support for negative temps

added todo list

simplify thread start syntax

add basic scaffolding for footswitch control

add code to suppress bogus temperature reports from the 1-wire interface

add support for second display for temperature and display dimming in film mode

clean up function names, use consistent threading syntax for both display and temp management

restructure temp measurement to remove infinite loop from inside thread and move out to caller

cleanup cruft in ds18b20 module