add a fwd.hh header with forward declarations of all classes

include/curves/fwd.h

+/**
+ * \file fwd.h
+ * \brief forward declaration of all curves class
+ * \author Pierre Fernbach
+ * \version 0.1
+ * \date 27/11/19
+ *
+ */
+
+#ifndef CURVES_FWD_H
+#define CURVES_FWD_H
+
+namespace curves {
+
+template <typename Time, typename Numeric, bool Safe, typename Point , typename Point_derivate >
+  struct curve_abc;
+
+template <typename Time, typename Numeric, bool Safe,typename Point >
+  struct bezier_curve;
+
+template <typename Time, typename Numeric, bool Safe,typename Point >
+  struct cubic_hermite_spline;
+
+template <typename Time, typename Numeric, bool Safe, typename Point ,
+            typename T_Point , typename SplineBase >
+  struct exact_cubic;
+
+template <typename Time, typename Numeric, bool Safe, typename Point,
+            typename T_Point, typename Curve, typename Point_derivate>
+  struct piecewise_curve;
+
+template <typename Time, typename Numeric, bool Safe,typename Point, typename T_Point>
+  struct polynomial;
+
+template <typename Time, typename Numeric, bool Safe>
+  struct SE3Curve;
+
+template <typename Time, typename Numeric, bool Safe>
+  struct SO3Linear;
+
+template <typename Numeric>
+  struct Bern;
+
+template <typename Point>
+  struct curve_constraints;
+
+template <typename Numeric, bool Safe>
+  struct linear_variable;
+
+template <typename Numeric>
+  struct quadratic_variable;
+}
+
+#endif // CURVES_FWD_H