Create a new signature by parsing the given buffer, which is
expected to be in the format "Real Name <email> timestamp tzoffset",
where timestamp is the number of seconds since the Unix epoch and
tzoffset is the timezone offset in hhmm format (note the lack
of a colon separator).
@param out_ new signature
@param buf signature string
@return 0 on success, or an error code
Create a new signature by parsing the given buffer, which is expected to be in the format "Real Name <email> timestamp tzoffset", where timestamp is the number of seconds since the Unix epoch and tzoffset is the timezone offset in hhmm format (note the lack of a colon separator).
@param out_ new signature @param buf signature string @return 0 on success, or an error code