For example, you have a pair of TGraphErrors objects:
"gStat" for the x,y values and statistical uncertainty ey;
"gSyst" for the same x,y values but with systematic uncertainty sy.

Usage of this class:
1. #include "MyHepData.h"
2. MyHepData Figure("x title", "x unit", gStat);
    // if you do not have a unit for x axis, then put empty string "" there.
    Figure.AddYaxis("y title", "y unit", gStat, gSyst);
    // if you have other curves (g1Stat, g1Syst) in the same plot with the same x axis, then
    // Figure.AddYaxis("y1 title", "y1 unit", g1Stat, g1Syst);
    Figure.Write("figure.yaml"); // to generate the YAML file

Notes:
1. You need write your submission.yaml by yourself anyway.
2. This class also support "qualifiers", but they are usually not necessary.
3. This class only includes public members for convenience, but be careful.
4. Drupal seems not to support *.h as attachemnt, so you need to rename it:
    mv MyHepData_h.txt MyHepData.h