Diary During Summer Vacation 13

Today, two new features have been added:
1) To make a string closed (G key): using method in CubicSpline class that I wrote during last session, a string can actually be closed (Knot_Log13_0.png, Knot_Log13_1.png). Here in our knot rendering engine, press G key is to switch the string from open to closed, and from closed to open as well.

2) To change string radius: The program is now able to change string radius in real-time (- Key to reduce and = Key to enlarge). See Knot_Log13_2.png - Knot_Log13_4.png.