return the interactive namespace for use in third-party libraries

An alternative proposal to integrate with IPython and other libraries.
This should be enough to support IPython usage, as described in issue #51.

Then you could probably setup your IPython environment with:

```python
import erppeek
import IPython

def main():
    global_vars = erppeek.main(interact=False)
    if global_vars:
        IPython.start_ipython(user_ns=global_vars, argv=[])

main()
```

I prefer this implementation because it does not rely explicitly on IPython. It is more generic.