Implement Circle header, rename all files to use .hpp extension.

include/J3ML/LinearAlgebra/AxisAngle.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <J3ML/LinearAlgebra/EulerAngle.hpp>
+#include <J3ML/LinearAlgebra/Quaternion.hpp>
+#include <J3ML/LinearAlgebra/AxisAngle.hpp>
+#include <J3ML/LinearAlgebra/Vector3.hpp>
+
+namespace J3ML::LinearAlgebra
+{
+
+    /// Transitional datatype, not useful for internal representation of rotation
+    /// But has uses for conversion and manipulation.
+    class AxisAngle {
+    public:
+        Vector3 axis;
+        float angle;
+    public:
+        AxisAngle();
+        explicit AxisAngle(const Quaternion& q);
+        explicit AxisAngle(const EulerAngle& e);
+
+        AxisAngle(const Vector3 &axis, float angle);
+
+        EulerAngle ToEulerAngleXYZ() const;
+
+        Quaternion ToQuaternion() const;
+        static AxisAngle FromEulerAngleXYZ(const EulerAngle&);
+    };
+}