Button handling library

The button handler uses the GPIOTE Handler to detect that a button has been pushed. To handle debouncing, it will start a timer in the GPIOTE event handler. The button will only be reported as pushed if the corresponding pin is still active when the timer expires. If there is a new GPIOTE event while the timer is running, the timer is restarted. Use the USE_SCHEDULER parameter of the APP_BUTTON_INIT() macro to select if the Scheduler is to be used or not.

The app_button module uses the app_timer module. The user must ensure that the queue in app_timer is large enough to hold the app_timer_stop() / app_timer_start() operations which will be executed on each event from GPIOTE module (2 operations), as well as other app_timer operations queued simultaneously in the application.

Even if the scheduler is not used, app_button.h will include app_scheduler.h, so when compiling, app_scheduler.h must be available in one of the compiler include paths.