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 !

The FindMuparser.cmake should also be updated. It currently fails to extract the version string from muParserDef.h, leading to errors in the configuration step, see #2071 (closed)