Add more specific metadata to request headers about search-tweets-python

[binaryaaron]

I like this enhancement and think we should do it in the make_session function.

We'll need to add the __version__ attribute to the module as well so we can grab it programmatically.

[binaryaaron]

#31 adds the __version__ variable to the module. @fionapigott - you can proceed with our header modification now. :)

Thanks!

[jrmontag]

Thanks @fionapigott!