allow configuring pypy

- enables bundled libzmq on pypy
- allows setup.py configure to work on pypy

copies compiler config json to zmq.utils, so they can be loaded by the CFFI backend.
test pypy bundled libzmq on travis
use travis pypy

it's no longer crazy old
link stdc++ in libzmq extension on PyPy on Linux

not sure why
Merge pull request #494 from minrk/configure-pypy

support configure and bundled libzmq on pypy