Change set_mode(),now the log file is optional and its name can be changed.

Do not use verbose logging in readpin.

Use getopt() for parameter input in dcf77pi, update usage information.
Update README.md with new parameters (command line and hardware.txt) and
reword some parts.
Overhaul readpin, instead of being a simple duplicate of dcf77pi it now
displays the raw GPIO values, taking the sample frequency and the minimum
second length into account.

This can be used to tweak hardware.txt and to optimize bit detection.