Peter M. Groen / libmodbus

- Use only addresses between address_start and address_end
- Better memory usage

- Major changes to unit-test-master/slave to add 4 tests
- Use new functions to manipulate bits
- Reduce memory usage (allocate only the required space and use
  uint[8|16]_t pointers)

- declare some functions static
- use uint8_t and uint16_t in various places to reduce memory use, the transition is not complete and will break compilation of some applications
- add some new functions to get/set bits from one or many bytes:
  o set_bits_from_byte
  o set_bits_from_bytes
  o get_byte_from_bits
- the server (slave) detects a connection closing

- Separate unit-test-master and test-master-random

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

Need testing.

- ModBus -> Modbus

- separate tests directory
- regroup modbus.h and modbus.c in the same dir
- updated waf scripts
- updated autotools files
- bump application version to 1.9.0
- bump library number to 2.0.0

- modbus.[ch] are LGPL
- test-modbus-master.c and test-modbus-slave.c are GPL

- Fix modbus.h path

- move modbus.h => include/modbus/
- create a pkgconfig file (module.pc)
- install modbus.h in $(includedir)
- new path to reach modbus.h

- Fix #191039 reported by Todd Denniston
    modbus.h is not installed at prefix