Add a fix for the numerical tests, where all compile definitions were overwritten by set_target_properties().

Exchange DEPENDS (which links everything private) variable with PUBLIC_LINK and PRIVATE_LINK. Therefore VirtualFluidsCPU is linking everything public know. Everything else is still linking private.

Add public target include directories to the cmake targets. Therefore the IncludeList.cmake files are not necessary anymore.
ADapt the export macros in the gks libraries.
Add 3rd/vtk helper cmake macro.
Gorup muparser into 3rd subfolder in visual studio project.

Make the cmake project more flexible while removing the CMAKE_SOURCE_DIR usage.

Make the cmake project more flexible while removing the CMAKE_SOURCE_DIR usage.

Remove unused stuff and the global include from VirtualFluidsDefinition.h. Adds missing export includes.

Adds authors and contributing file. Clean up the readme file.
Set the minimum cmake version to 3.13 according to the readme entry.
Set the options BUILD_VF_CPU, BUILD_VF_GPU and BUILD_VF_UNIT_TEST to OFF by default.

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https://stackoverflow.com/questions/31673945/clang-backslash-and-newline-separated-by-space-in-single-line-comment