Peter M. Groen / libmodbus

This reverts commit df0cf7927249954f15e0aa85b02d21b990fa9af9.
Use <modbus.h> in tests.

Some files reference modbus.pc or modbus.pc.in while other files
reference libmodbus.pc or libmodbus.pc.in.

Let stick with libmodbus.pc or libmodbus.pc.in.

This time the change is definitive :)

- upgrade to WAF 1.5.3
- smaller WAF scripts
- fix using of modbus.h with WAF
- updated configure.ac and Makefile.am files
- change include paths in test files

- Add test files to examples directory in libmodbus-dev.
- Add MIGRATION file to libmodbus-dev.
- Define the compatibility level to 6.
- Add MIGRATION to EXTRA_DIST in Makefile.am
- Add README to  EXTRA_DIST in tests/Makefile.am
- Add unit-test.h as dependency in tests/Makefile.am

- 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

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

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