Don't want to add a configure script for this, so to aid portability and avoid having to link to libbsd pretend we don't have these two niceties. err/warn are still in use and won't be removed.

allow to print also 7 and 8 digits long codes in addition to the current defaut of 6. Requested by heph

it shouldn't EVER be needed, but since we handle URIs we should tick this box too.

More often than not, services provide the URI for TOTP and not the raw secret. While it's easy to manually extract the secret from the querystring, teach totp how to do that on behalf of the user. Manpage bits will follow. Discussed with heph.

no need to take an explicit length parameter when we can just advance the string until a NUL byte. base32 doesn't allow NUL bytes.