Implement Axisangle::ToQuaternion, and AxisAngle constructor from matrix

src/J3ML/LinearAlgebra/AxisAngle.cpp

@@ -20,4 +20,8 @@ namespace J3ML::LinearAlgebra {
         axis = a.axis;
         angle = a.angle;
     }
+
+    Quaternion AxisAngle::ToQuaternion() const { return Quaternion(*this); }
+
+    AxisAngle::AxisAngle(const Matrix3x3 &m) : AxisAngle(Quaternion(m)) { }
 }