This patch introduces a basic on disk configuration, comprised of a main
configuration file and per-domain directories.
It's still not complete, but will be extended in subsequent patches.
This patch introduces a general connection timeout (20m); and a shorter one
(1m) for individual command round-trips.
DATA is excluded from the latter, because it is expected that it takes more
time; we use the general connection timeout for it.
This patch adds some tests that cover the SMTP commands, including STARTTLS
and various correctness checks.
There are also two simple benchmarks, that are not optimized and are more
useful for stress testing and profiling than anything else.
