variable: server-default-port
procedure: server-exception-handler key a ... ->
ignore socket io errors (for example connections closed by peers).
exceptions can be raised by rnrs raise or guile throw
variable: server-listen-queue-length
procedure: server-socket address #:port #:type #:protocol #:set-options #:non-blocking ->
create a socket with default options. the socket type is inferred
from the address, which can be an ip4 or ip6 address (tcp) or a filesystem path (unix socket)