Add an option to specify the private DO slot where the key is
to be read, instead of always using private DO #1.
Note that reading from private DOs 3 and 4 will fail if the
appriopriate PIN has not been verified prior the call to
Add a new tool, scdtotp, to use the OpenPGP smartcard as a poor
man’s one-time password token. The program reads a key from
the smartcard’s private DO and derives and time-based one-time
password from it.