parameters & wrapper

- new parameter class :
  parameters are viewed as form, built in C++, and filled in C++/python.
  Each field of the form as a precise C++ type (erased using standard techniques).
  First tests ok, to be reread/checked.

  TODO : serialization is commented. Lead to long compilation time & large code
  due to boost::serialization. Use h5 when possible.

- wrapper :
  - separated the converters of the wrapped type in the TRIQS library
  - necessary for parameters (it used outside an .so) and potentially
    other codes, outside an .so module