Fix duplicate callback on qos2 (#194)

Verify if the message isn't already in the list before adding it (qos 2).
Messages with the same mid are considered equal.
Signed-off-by: NKelvin Nogueira <kelvin.elton@gmail.com>

Add exponential reconnection delay

tls_set_context and enable_logger were the only two methods
without their defaults in method signatures.

Make test suite a bit more strict

Only pyflakes is enabled for now
Signed-off-by: NMichael Boulton <boulton@zoetrope.io>

Arbitrary websocket headers

Tidy develop branch

also separate out the header joining into a function

http://pytest.org/dev/yieldfixture.html

    With pytest fixture functions, the “after yield” part will always be invoked, independently from the exception status of the test function which uses the fixture.

Use socketserver to make a temporary server which websocket tests can be run against, which takes data to return.

Probably needs extending so more checking can be done on the path etc.

Signed-off-by: NJames Myatt <james@jamesmyatt.co.uk>

Note that MQTT v5 also uses protocol name = "MQTT"
Signed-off-by: NJames Myatt <james@jamesmyatt.co.uk>

Signed-off-by: NJames Myatt <james@jamesmyatt.co.uk>

Signed-off-by: NJames Myatt <james@jamesmyatt.co.uk>

Now contains a more full example of how to connect to AWS IoT platform and points to it in the documentation.