Merge adds a new macro
HYTEG_ARCH_ENDIANESS to HytegDefinitions that is set by CMake to the value of
CMAKE_CXX_BYTE_ORDER. We also add a query method
systemEndianess() to BuildInfo. We use this information then to place the correct information into our VTU output files, instead of hardcoding LittleEndian everywhere.
In order to use the CMake macro we need 3.20 as minimal version and document this in our README.