
---- Modify Mean_v2 and use STL ----

Replace native arrays with STL "vectors" in the class "Event",
as described in the following.

***
Modify the class "Event":
- replace the array of pointers with a std::vector ,
- remove the number of particles, corresponding to the size of the vector,
- remove the maximum number of particles,
- modify the member functions to use the vector in place of the native array.
In the constructor reserve for the vector a number of elements equal to 10.

***
Modify the "main" function to use a std::string for the input file name.

********* final list of functions *********

main                   modify Mean_v2
read                   copy   Mean_v2
dump                   copy   Mean_v2
mass                   copy   Mean_v2

********* final list of classes   *********

                       .h                            .cc
Event                  modify Mean_v2                modify Mean_v2
MassMean               copy   Mean_v2                copy   Mean_v2
Constants              copy   Mean_v2                copy   Mean_v2
Utilities              copy   Mean_v2                copy   Mean_v2
