Peter M. Groen / libmodbus

- remove doc build from autotools
- don't depend anymore on asciidoc
- don't provide man pages anymore
- new illustrations
- provide mkdocs instructions

Fix #513

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

They are already included in these Linux distributions.

- 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

- depends of automake 1.11
- C99
- pic-only
- more warning C flags
- remove obscure checks
- don't print directories
- add libmodbus.pc to clean files
- remove -Werror

Each function is decribed in one txt file. The file libmodbus.txt
offers an overview of the library.

It's possible to generate HTML and man outputs from the txt file.
The documentation can be generated only if you have the required
tools (asciidoc and xmlto).

Better results are obtained with AsciiDoc v8.6+

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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