Time correlation example : Not ready to merge

Example for one time correlation with real XPCS data. Plot the correlation functions
The following code will unzip your zip file

```python

    #  image data as a stack
    fname = "img_stack5301_5401.npy"
    try:
        img_stack = np.load(fname)
    except IOError:
        zipfile.ZipFile(fname + '.zip').extractall()
        img_stack = np.load(fname)
```