Fix warnings when generating the cpp programmer's reference

When building the cpp part of the programmer's reference we currently get 50 warnings. The warnings are related to the signatures:

overloading 'operator'
operator>>
operator<<
operator--
operator++
operator->

ellipsis in arguments
/home/oelgaard/software/fenics/fenics-doc/source/programmers-reference/cpp/log/log.rst:52: WARNING: Invalid definition: expected name [error at 28]
  void begin(std::string msg, ...)

and passing arrays as arguments
/home/oelgaard/software/fenics/fenics-doc/source/programmers-reference/cpp/ode/ComplexODE.rst:55: WARNING: Invalid definition: expected comma between arguments [error at 22]
  void M(const complex x[], complex y[], const complex z[], real t)