Use package name when __main__.py is used #76

I'm investigating how to package a single file application with fire at the moment.

It seems that in order to have pip install the requirements, a setup.py files needs to exist. And setup.py requires that a package be defined. When this is done, a file, __main__.py is created in the package directory and invoked using, python -m mypackage COMMAND.

In this case the logic is in mypackage/__main__.py, which, when used with fire shows __main__.py in the usage output, where mypackage display is desirable.