Runtime error during module import

Uncomment the last line `sys.exit(app.exec())` in `example1.py` to workaround #3 and run
```
$ python example1.py
```
Output:
```
Traceback (most recent call last):
  File "example1.py", line 5, in <module>
    from qcustomplot import QCustomPlot, QCPBars, QCP
ImportError: /usr/local/lib/python2.7/dist-packages/qcustomplot.so: undefined symbol: _ZTI14QCPItemBracket
```