* The code is built with -Werror and newer gccs warn on implicit
  fallthrough with -Wall -Wextra, so the build failed.

* The build failed with linker errors with gcc 8.3 (the inline
  functions could not be linked against).

* The inline annotation were removed accordingly from functions
  that are linked, while those that are only used within one
  compilation unit were marked static inline instead.

* make -B did not work, because ln -s failed on existing links –
  fixed by using -f.

* Make the main loop non busy (use wfi instead).

* Make the touch sampling interrupt driven.

* Note: When starting with BURST_SWMODE there seem to be no ADC ready
  interrupts, so we use HWSCANMODE although we only want to sample once
  and disable the ADC in the interrupt handler.

* Open question: Is there a point in not just sampling the touch screen
  in the main loop every 50ms and have the main loop wfi and be awoken
  by the systick interrupt (the ADC is pretty quick, 11 clocks of the ADC
  clock, which is 4MHz, so just 132 CPU clocks, and less than even
  a signle bit over the UART at 115200 baud). It may well be that the
  interrupt driven method burns more cycles while only marginally
  improving responsiveness (if at all).