quaternion<T>::rotationQuat(const vector<T, 3>& axis, T radians)

[HuazyYang]

The implement as following

	template<typename T>
	quaternion<T> rotationQuat(const vector<T, 3>& axis, T radians)
	{
		// Note: assumes axis is normalized
		T sinHalfTheta = std::sin(T(0.5) * radians);
		T cosHalfTheta = std::cos(T(0.5) * radians);

		return quaternion<T>(cosHalfTheta, axis * sinHalfTheta);
	}

calling quaternion<T>::quaternion(T w, const vector<T, 3> &v) which does not exist obviously at all. so quaternion may need this constructor.