move cores to zmq.backend.[implementation]
update imports for new backend location
bump version to 14

for the reorg - zero public APIs have been touched,
but any remaining bad code that imported directly from `zmq.core` is broken by the change.
add backend.select, __init__

forgot to add them in the last commit
ignore new generated Cython location
add explicit poll interval in zmq.green

workaround same gevent FD bug in the sockets

closes #370
Merge pull request #372 from minrk/gevent-poll-bug

add explicit poll interval in zmq.green.Poller

workaround same gevent FD bug in the sockets

closes #370
Merge pull request #371 from minrk/backends

move cores to zmq.backend.[implementation]

Makes a bit more sense this way.

Version is bumped to 14.0.dev, because of the reorg. Zero public APIs are touched, but any remaining bad code that imported directly from zmq.core is now totally broken.
CFFI capitalization
performance tweaks for Poller

before, peaked around 50k msgs/sec, after around 110k msgs/sec
performance tweaks for socket

don't deep-inspect closed state on every method, only the `closed` property.
fix unregistration with new list

unregister is now up to O(N), but that's much better than poll() being so.
Poller.sockets is a list
add `Poller.__contains__`

and use it in a test, rather than giving the appearance that `sockets` is a public API.
Merge pull request #380 from minrk/caps

CFFI capitalization
Merge pull request #381 from minrk/pollperf

minor performance tweaks to poller

Give a ~2x improvement for the simple case of a single Socket on my laptop (2.5 GHz i5, OS X 10.8.4).

- before: around 55k msgs/sec
- after: around 110k msgs/sec
Remove unhelpful GIL releases

We used to release the GIL on all libzmq API calls, but many of these calls are not blocking. Since there is a finite cost to GIL transactions, I have removed the GIL releases that are not on blocking calls.

Simple testing shows a notable improvement in performance for multithreaded apps (simultaneous `while True: send/recv` threads).
Merge pull request #383 from minrk/giltest

Remove unhelpful GIL releases

We used to release the GIL on all libzmq API calls, but many of these calls are not blocking. Since there is a finite cost to GIL transactions, I have removed the GIL releases that are not on blocking calls.

Simple testing shows a notable improvement in performance for multithreaded apps (simultaneous `while True: send/recv` threads).
corrected typo in docstring
Merge pull request #386 from iyedb/patch-1

corrected typo in docstring