Always use get and put

[richelbilderbeek]

Here is the thread:

https://www.reddit.com/r/cpp/comments/3xw5q0/a_wellconnected_c11_boostgraph_tutorial/

From mat69:

• You are not consistent in the way you access property maps. Sometimes you use my_map[XYZ] and other times get. To have flexible code you should always use get and put. That way you can change the vertex storage from vector to something else, without having to adapt all the other code.

[richelbilderbeek]

Done