Peter M. Groen / libmodbus

- only check if documentation tools are installed in acinclude.m4
- don't provide built documentation in dist tarball
- simpler Makefile
- display warning message and check result

It concerns only the files in 'tests' directory.

- protect against NULL IP address BTW
- update documentation

- allow an empty string or NULL for node argument
- protect against NULL in service argument
- new test for NULL service
- update documentation

Change API of function for libmodbus v3.2.0

The report slave id function returns the number of bytes as the _return_
value, and does not include it as the first byte in the dest buffer.

Update documentation to reflect reality.  There's no missing
functionality, just slightly confusing documentation.

- add byte timeout tests (TCP backend only)
- update and improve documentation
- long timeout values are now uint32_t so it changes the API
  to disable byte timeout

- update documentation
- 5 new tests
- updated NEWS file
- avoid include of time.h

Related to https://github.com/stephane/libmodbus/issues/83

- change return argument from void to int
- update documentation

Thanks to Karl Palsson.

Thanks to Mirko Rajkovaca

Thanks to Bill Gray.

Warning, modbus_receive returns 0 when a query is ignored.

- function removed from TCP and RTU code and from backend structure
- updated documentation
- updated examples