remove the embedded copy of six.py, use dependency instead
update Makefile instructions, setup process

We rely on setup.py's install_requires= for everything except scrypt,
which has some sort of packaging bug that makes it not work unless
installed directly with pip. (scrypt is only used by fxa-vectors, to
compute values that live on the fxa-auth-server backend).
don't install bin/fxa-vectors, just run it from source

The scrypt packaging bug means that "pip install fxa-python-client"
probably won't give you a functional fxa-vectors anyways, so avoid
confusion by not installing it. The preferred way to build test vectors
is to run "make vectors" from a source checkout.
README: explain the purpose a bit better
release version 1.0.0