Peter M. Groen / libmodbus

- change return argument from void to int
- update documentation

Thanks to Karl Palsson.

DLL if required.

Thanks to Petr Gladkiy

Thank you Petr Gladkiy

Thanks to oldfaber and endrelovas.

Simply run cscript configure.js from the win32 directory to generate
the files needed to create the modbus DLL.

Thanks Tobias Doerffel.

It will better to code something such as:
https://github.com/crossroads-io/libxs/blob/master/src/err.cpp

I don't intend to rewrite glib neither :(

Thanks Giampaolo Bellini.

- 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

Add standalone Makefiles for the modbus DLL and tests, using the modbus DLL.

Thanks to Denis Davydov

Fix EXXX values defined in Microsoft C Runtime 10

Thanks to Carlos Tangerino

Thanks to oldfaber