Use `if __name__ == '__main__':` as an entry point

[khatchad]

I suspect that if __name__ == '__main__': is not being considered as an entry point. Using it and not using it on the same examples gives me a different IR and CFGs. Seems related to #17.

[khatchad]

On the example I tried, by removing if __name__ == main:, I am getting four more basic blocks than I had previously. The corresponding call graph node is that of import() (very early in the CG).

[khatchad]

if __name__ == '__main__': is used to block out code that won't execute if the module is imported instead of executed from my understanding.