Update 'morse_types.h' header to allow its use from C++ code
Add option to allow users' applications to redefine C complex types to C++ complex types (which are binary compatible with C complex types)
The library Fabulous ( git clone https://scm.gforge.inria.fr/anonscm/git/ib-bgmres-dr/ib-bgmres-dr.git --branch develop fabulous ) use Chameleon and is written in C++. Thus, it needs that chameleon header work with C++ complex types (in the same way it is done in LAPACKE header: see https://gitlab.inria.fr/solverstack/chameleon/blob/master/coreblas/include/lapacke_config.h#L91)
Limitations of this commit is that the codebase that would be using it not very wide yet (probably just Fabulous for now).
Therefore, this needs thorough reviewing and suggestions.