Closes #500. Closes #89.

Closes #520. Thanks to Chris Hibberd.

Closes #566. Thanks to Cody Scott.

Appending to bytes() is slow, bytearray() is fast.

Closes #571. Thanks to Umberto Morelli.

It would sometimes call the MQTT v3.x callback when it should
call the MQTT v5 callback.

Closes #570. Thanks to Frank Pagliughi.

Closes #575. Thanks to briggySmalls.

And convert the _out_packet queue use to thread safe.

Closes #409
Closes #576
Thanks to Thomas Zahari.

The `rc` parameter in the `on_disconnect` callback now has meaningful values
in the case of an error. Closes #441. Thanks to Nawab.

This means that outgoing messages will only be retried on the client
reconnecting to the server. They will *not* be retried when the client
is still connected.

The correct usage for `socket.create_connection` is below:

>> socket.create_connection(address[, timeout[, source_address]])
>> Connect to a TCP service listening on the Internet address (a 2-tuple (host, port)), and return the socket object. This is a higher-level function than socket.connect(): if host is a non-numeric hostname, it will try to resolve it for both AF_INET and AF_INET6, and then try to connect to all possible addresses in turn until a connection succeeds. This makes it easy to write clients that are compatible to both IPv4 and IPv6.

>> Passing the optional timeout parameter will set the timeout on the socket instance before attempting to connect. If no timeout is supplied, the global default timeout setting returned by getdefaulttimeout() is used.

>> If supplied, source_address must be a 2-tuple (host, port) for the socket to bind to as its source address before connecting. If host or port are ‘’ or 0 respectively the OS default behavior will be used.

>> Changed in version 3.2: source_address was added.

Also the semantic of connect timeout and keepalive timeout are totally
different.

Signed-off-by: NMax Christoph <chrystler@web.de>

Signed-off-by: NBert Kleewein <bertk@microsoft.com>

Closes #551.

Signed-off-by: NFrederik Aalund <fpa@sbtinstruments.com>

Closes #481. Thanks to Tao Su.

They can optionally be suppressed by setting `client.suppress_exceptions = True`.

Closes #365.

Signed-off-by: Nkoho <gerhard.gh.ta@gmail.com>

Fix wrong variable assignments (they worked as comparisons instead). Remove comparison to boolean value
Signed-off-by: NBor Gonzalez-Usach <bor.gonzalez.usach@contact-software.com>

Signed-off-by: NMarcin Jaworski <marcin@jaworski.me>

Signed-off-by: NMarcin Jaworski <marcin@jaworski.me>

Signed-off-by: NJosiah Witheford <josiah.witheford@gmail.com>

If an exception was raised in a filtered callback function, the main thread would crash.
Signed-off-by: NJosiah Witheford <josiah.witheford@gmail.com>

Closes #410