debounce buttons with a non-memorizing startup delay based on `std::thread`

[dhebbeker]

Introduce a new Worker class which is a wrapper around a std::thread and:

• allows for a delayed start of the actual work
• allows to abort while still in the start delay
• provides a getter to see if the thread is finished (without the need to join()

Resolves #113.

[dhebbeker]

My current attempt (f61d16bf3f29ddf3fdf1f871570fb94ebd1a93bd) is problematic as using functions from the C++ Standard Library within an ISR can cause problems.

For debouncing I may simply use millis(). But the question remains on how to do the actual work if I don't want to do this in the context of the ISR nor by starting a std::thread directly from within an ISR.

[dhebbeker]

See also:

• Using xQueueOverwriteFromISR() from ISR: https://github.com/sandeepmistry/arduino-LoRa/issues/224#issuecomment-488434092
• xTaskNotifyFromISR()
• ulTaskNotifyTake()
• Recommendation for using vTaskNotifyGiveFromISR 👀
• FreeRTOS Queues

[dhebbeker]

I moved the thread management outside of the ISR into a separate thread which continuously polls for signals set by the ISR. The signals are set by the ISR using std::atomic_flag which are lock-free.

This works in general. But it means that we have a polling thread which is not a good design (comment 1, comment 2, article (did not read yet)). It may become a problem when we want to use sleep modes for the processor for power saving. 🔋

[dhebbeker]

This is closed in favour of #116 which does not rely on polling.