Peter M. Groen / libmodbus

Reported and tested by Yishin Li.

Real fix #333455 - IPTOS_LOWDELAY not supported on cygwin
Thank to Yishin Li for the better problem description.

- check IPTOS_LOWDELAY define in configure
- generate a config.h
- include the generated config.h in modbus.c

- MAJOR changes to the API (see MIGRATION)
- New unit tests
- Removed TODO list
- Updated NEWS & MIGRATION files

- remove header and checksum length from modbus_param_t
- use new const tables

Invalid error check in modbus_init_listen_tcp

modbus_check_response() crashes on an invalid exception code

- Update the NEWS file

It is easier to install on rpm based systems with a spec file.

I don't want to update the file to each beta until the 2.0 release so
I already use the 2.0 name in the spec file.

libmodbus does not link with c++ code.

With TCP, automatic reconnect on error may not be desired.
It's now possible to adjust the error handling mode.

- ModBus -> Modbus

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