Implement the algorithm to dynamically determine the boundary values as described in 2a8e6472cd0aa12fee8b363c231b4c0430061866

The difference with readpin.c is that maxone is updated once per second
instead of once per minute, giving a faster response in case of sudden
changes to realfreq.

Drop the case that tlow /t  is uninitialized.
Add a third state to "init" (2) to indicate that a bit has been received but its length (in samples) is still untrustworthy.

Only update "bit0" and "bit20" if a bit is properly received.
Update the display (and fix after 0f81fce9a02a680085b172ecc1caf04f33bc08f2):
- Show bit0 and bit20
- Show maxone as percentage
- Show "OK" if the radio state is OK (no receive/transmit/random/IO error)
- Widen the fraction field to show the first digit of tlow / t
- Shorten the realfreq field to make the line fit in 80 characters
- Rearrange the field order
Remove hw.maxzero and hw.maxone from the code and from config.txt
Remove maxzero and maxone from README.md