Update MuParser version in Superbuild
MuParser 2.3.2 is available. Notable changes are :
- MuParser now uses C++ 11
- MuParser is now a CMake project.
Superbuild should be updated to use this new version. Currently a CMakeList.txt file is provided to the Superbuild to compile the library as a CMake project. This can be simplified as Muparser is now a CMake project !