Fixes #286

Dan and Claudio are not active contributors any more.

soup_session_new() returns a new GObject, so it should be marked
as "transfer full"

They can just be get from the connection.

Emitted when the connection is connected and the TLS handshake
completed. Use connection connected signal to set the IO data.

Client list is now a list of connections, owned by the server. The
connection creates the messages and notifies the server with
request-started signal. The first message is created before the TLS
handshake, and then request-started is emitted to allow the user to
connect to accept-certificate signal on the message. If the connection
is persistent, the next request-started signal will be emitted if
there's an actual request from the client. This is a change in behavior,
before we always emitted the request-started when waiting for a new
request even if the request never actually started.

Now that we have connected and request-started signals in the
connection, we no longer need the setup async function, we can just
notify the connection that it's been accepted and do the setup and tls
handshake.

They don't use the server at all, they just call
soup_server_message_pause/unpause, so we can make them public instead.

For now the plan is to use it only for testing the client APIs.

Message finish can destroy the server io.

We need to ensure that deprecated and unavailable symbols are still
exported, so we should use our own symbol.

While at it, the deprecation warnings should be toggleable.

This way we ensure every symbol gets exported, even when deprecated, and
that deprecation warnings can be disabled.

Closes #295