Add shared library to build targets

[stlehmann]

This PR resolves #284 by adding a shared library to the build targets. The compiled adslib.so is used by pyads, a thin Python wrapper for ADS.

The PR contains these changes:

• set .gitattributes to set eol character to LF
• add extern "C" statement to prevent name mangling. This is needed to access the functions by their proper names in the shared library.
• Add a new build target to meson: adslib.so

[pbruenn]

@stlehmann unfortunately, its not so simple. This completely breaks the build for "-DUSE_TWINCAT_ROUTER". I try to fix that and I will squash most of your commits. especially the fixups.

[pbruenn]

@stlehmann please take a look at https://github.com/Beckhoff/ADS/tree/patrickbr/for-stlehmann-pyads-integration.

Is that working for your usecase?

The biggest problem with your original approach is that we have a more const correct API here in the standalone version, but when this is build with the original TwinCAT headers everything breaks as long as we use the same names for the exported C functions.

EDIT: Do we need this? c08e11c

[stlehmann]

@pbruenn this looks great. Somehow I still get symbol errors for AdsAddRoute and AdsGetLocalAddressEx. I still try to figure out the reason for this.

[pbruenn]

@pbruenn this looks great. Somehow I still get symbol errors for AdsAddRoute and AdsGetLocalAddressEx. I still try to figure out the reason for this.

Arg maybe because of this... 48ac1f2