New error function API (LossFunction) about april-ann HOT 1 CLOSED

  class LossFunction : public Referenced {
  protected:
    Token *error_output;
    unsigned int size;
  public:
    LossFunction(unsigned int size) :
    Referenced(), error_output(0), size(size) {
      if (size == 0)
        ERROR_EXIT(128, "Impossible to build ZERO size LossFunction\n");
    }
    virtual ~LossFunction() {
      if (error_output) DecRef(error_output);
    }
    virtual float  addLoss(Token *input, Token *target) = 0;
    virtual Token *computeGrandient(Token *input, Token *target) = 0;
    virtual float  getAccumLoss() = 0;
    virtual void   reset() {
      if (error_output) DecRef(error_output);
      error_output = 0;
    }
  };