[tor-dev] Tor Export

Hi Damian,

Here is a first draft for the tor export module we have been discussing. I have attached the file as we were having some git issues and I am in a bit of a rush right now. We have been developing the file at stem/descriptors/export.py. Any suggestions or comments would be appreciated -- we have done basic testing, and would be happy to implement some unit & integration tests if this implementation satisfies the needs of the community.

Thanks, Erik and Megan.