Printing can take a lot of time over a serial connection. On the atmega
board it takes more than 2 ms, skewing the first measurement over the
threshold value and causing a test failure. This moves the print
statement above the first measumerement to prevent the skew.
- adapt code to use public, typesafe API calls
- add some statistical output
- minor code enhancements and doc corrections
- use fmt print_str for uint64_t
