The construction of an EventHandler object should not be directly done
by the client. Instead, it is easier to use procedural macro to
automatize the process, hence exposing a nice and simple interface. Such
use of procedural macros requires to crate an additional crate.
The timestamp comes from OpenBSD's struct timeval, which defines the
number of seconds as a time_t (i64) and the number of micro-seconds as a
suseconds_t (long, hence i64 too). They are separated by a dot.
https://man.openbsd.org/gettimeofday.2
The latest OpenSMTPD draft added the timeout event, it therefore has
been added to the parser. As shown in the new sessions examples, the
timestamp format changed and the parameters are also optional.
