Peter M. Groen / libmodbus

- 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

Add macros in libmodbus.txt and:
- modbus_get_byte_from_bits.txt
- modbus_get_float.txt
- modbus_reply.txt
- modbus_reply_exception.txt
- modbus_set_bits_from_byte.txt
- modbus_set_bits_from_bytes.txt
- modbus_set_float.txt

Avoid incompatibility with GPLv2 program. This change has been approved by
Tobias Doerffel, Florian octo Forster and Hannu Vuolasaho.