输入一个旋转角度，以及一个旋转轴，可以求出空间中任意点的旋转矩阵 注意角度用弧度单位-Given input: r: angle to rotate, in rads Axis: axis of rotation, defined as a 3point which connects to the origin. Output: 3x3 Matrix R such that for an arbitrary point v, Rv is the poi