Make the build using all files in one, also c files
Add line numbers to temp.ino

This sohuld help gcc give better feedback on compilation errors!
More appropriate handling of key press
_Static_assert isn't always available.

Commenting out until now, we should find an approach that is handled by both
gcc and g++...
Make i a uint16_t (84 * 48 > sizeof i)
Correct signature on alarm_set_timestamp
Use the typedef read_function_t for readability