Peter M. Groen / libmodbus

Since SPDX release 3.0 LGPL-2.1+ became LGPL-2.1-or-later. Hence
replace the deprecated identifiers.

Thanks to @JCWren

Current code could dereference NULL pointer in case an inner
malloc fails. Check for this and exit gracefully.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

EMBBADCRC, not EMBADCRC

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

This replaces the lengthy license text headers with a short
and standardized license tag. See http://spdx.org for details.

This is useful e.g. for license compliance tools which scan
through files and generate a report of the licenses used
in a project.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

Thanks to Marjan Tomas

Thank you AlexMaz.

Thanks to Jan Kardell.

- change return argument from void to int
- update documentation

Thanks Giampaolo Bellini.

Original patch provided by Michael Haberler <git@mah.priv.at>.

Original patch for new connect function by Thomas Stalder.

- export new symbols to create specific behavior (RTU)
- the flag can't only be set by slaves
- new tests