0.5.0

• Breaking: the words are the stack's own. connect's, Listener.connect's and Pool.create's ~clock is ~mono_clock, Listener.connect's ?heartbeat is ?keep_alive, and reset, which reconnects, is revive; Pool.create's ?reset, which cleans a session, keeps its name.
• Breaking: Postgres_eio.error is a polymorphic variant, as Pool.use's errors already were, and every function that fails answers [> error], so a connection's failures and a pool's join in one result. Timeout, Io and Protocol are one tag, `Lost: the statement was sent and no answer came back, so it may have run. Closed is `Connection `Closed and now means the statement was never sent: an answer a close or a failure leaves unread is `Lost. A connection that cannot be made, by connect, revive, Listener.connect or Pool.create, answers `Unsent for what was Timeout, Io or Protocol, since nothing was done. Server and Refused are `Server and `Refused. Pool.error_to_string prints a connection's errors as well as the pool's.
• A SCRAM sign-in whose server asks for more than a million iterations is refused before the first. The count was unbounded, and computing it never yields, so a server asking for a hundred million held the connect, its timeout and every fiber on its domain for over a minute.
• A Pool.create cancelled partway closes the connections it had made. They were left open, sessions held at the server, until their switch ended.
• connect_timeout bounds a host's name lookup. eio_posix looks a name up in a system thread no cancellation reaches, so a slow resolver held connect for as long as it took; the lookup now runs beside the wait, on the connection's switch, and is left to finish there. A Postgres_eio.Resolver, which connect and Listener.connect take as ?resolver, does lookups on its own fiber for a connection revived on any domain, since Eio forks onto a switch only from its own; a pool keeps one for its connections, so a borrower's revive is bounded on every domain.
• Breaking: every connection, a Listener's too, sets the settings the decoders read text by -- client_encoding=UTF8, DateStyle=ISO, IntervalStyle=postgres and extra_float_digits=3 -- over a database's and a role's defaults. Nothing set client_encoding, so in a LATIN1 database UTF-8 text was stored as mojibake, and with extra_float_digits=0 a float read back rounded. A parameter or an options setting giving one of them another value is `Refused; client_encoding is compared by encoding, so UTF-8 or Unicode is UTF8.
• Breaking: with no sslmode, a host on another machine needs TLS, and only a host on this one -- localhost, 127.0.0.0/8, ::1 or a Unix socket, judged by hostaddr when given -- is prefer. Every host was prefer, so a server that declined TLS, or a network that stripped it, had the password and every query sent in the clear. A server that offers no TLS is refused with an error naming sslmode=disable and prefer. sslnegotiation=direct with no sslmode needs TLS of every host. Conninfo.t's ssl_mode is an option, None when the string gives none, and each Conninfo.endpoint has the ssl_mode it is reached with.
• Breaking: sslrootcert is refused unless sslmode is verify-full or verify-ca, the only modes that read it: with any other, or none, the file was silently ignored and no certificate checked. Write sslmode=verify-full, or verify-ca, to check against it.