Closes #2032.

Closes #2130. Thanks to becz.

Closes #2123. Thanks to quackgizmo.

Closes #2111. Thanks to yellowgg2.

It was setting the exact TLS version to use, not the minimium TLS
version to use.

Closes #2110. Thanks to Petter Jönsson.

Remove use of environment variable, instruct users to run a specific
command instead.

Signed-off-by: Abilio Marques <abiliojr@gmail.com>

Closes #2096. Thanks to blusewang.

Provide a mechanism for Docker users to run a broker that doesn't use
authentication, without having to provide their own configuration file.

Closes #2040.

The would not return MOSQ_ERR_INVAL on topic == NULL.

If it is compiled without external poll support.

Closes #2060. Thanks to Yannic Schröder.

Closes #2078. Thanks to Ysincit.

If we do that, then nothing can connect even from the local machine.

Closes #2066. Thanks to Boris Vanhoof.

Closes #2057. Thanks to Przemysław Zygmunt.

Closes #2059. Thanks to Jason White.

Closes #2056. Thanks to Greg Troxel.

This now handles the case where we are building from the released tar, or
building from git if xsltproc is available, or building from git if xsltproc
is not available.