Remove VirtualFluidsDefinitions.h header file.
Remove redundant compiler definitions from gpu.cmake.

Make use of the new cmake command: target_link_options, target_compile_options and target_compile_definitions.

Move VirtualFluids header to src.
Add CI file and add files, only existing in the open source version.

Therefore the muparser cmakeLists.txt was used, but a modified:
 - name is corresponding to the original file: muparser (in lowercases)
 - removed the install
 - adds public include directory : CMAKE_CURRENT_SOURCE_DIR/include.  --> also adapt the include from the dependent fles.
 - adds link to OpemMP

CXX 11 is now required. (CMake throws an error if cpp11 is not available).

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.

Increase required version to 3.18 and set the cmake policy CMPI0104 to NEW. Therefore the CMAKE_CUDA_ARCHITECTURES needs to be set.

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.

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

Changed the setting the compiler options to the new cmake function: target_compile_options