Merge branch 'regression-check-vs-uncover-issue' of https://github.com/JuergenKosel/paho.mqtt.c into fixes

Proposed patch: simplify handling of thread libraries on Unix-like OSes

Documentation updates

Squashed commit of the following:

commit 907b9ecdaf160bf95c17aafcaf4ab3e656ab9ccc
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Wed Apr 5 23:33:44 2017 +0100

    Use binary passwords in tests

commit 3930b18d3835727e3cb98ef0ce1a742bd0dffab7
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Wed Apr 5 17:15:29 2017 +0100

    Binary MQTT password support

commit 4abe6a996b1219aafa22b5dd69bf1e676d377466
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Wed Apr 5 16:13:18 2017 +0100

    Fix test config

commit e742ed182d6de44e9afd6e9c9c03c79f359fbe29
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Wed Apr 5 15:46:53 2017 +0100

    Async binary will message

commit 9313e66214720c285f510e325a5c942ad22f2542
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Wed Apr 5 11:50:10 2017 +0100

    Binary will message support, take 2

commit 5cf548505a548eff394348aa7406e5a34d0f5054
Author: Ian Craggs <icraggs@uk.ibm.com>
Date:   Tue Apr 4 22:54:15 2017 +0100

    Binary will message

Signed-off-by: Otavio Rodolfo Piske <opiske@redhat.com>

Signed-off-by: Otavio Rodolfo Piske <opiske@redhat.com>