Break out customized exporter

[cab938]

I think it would be good to have a second example which might just be in the docs about how to write your own customized exporter. When I look at the code you have it wasn't immediately clear to me (though should have been!) that this was just showing a custom function the end user could write:

def customized_exporter(args):
    # do more here
    return ({
        'exporter': 'CustomizedCommandLineExporter',
    })
...
    {
        'exporter': customized_exporter,
        'args': {
            # do more here
        }
     },```

Could we put this somewhere in the documentation instead of in a code file? Alternatively, would could have multiple configuration_examples:

\configuration_examples\:
     \simple_console_logging\
     \logging_to_browser\
     \custom_function\

WDYT?

[mengyanw]

Sounds great! I will work on it :)

[mengyanw]

Configuration file examples added.