README is now markdown

Build/Install and Release instructions moved to Wiki
Merge pull request #306 from minrk/readmemd

README is now markdown

Build/Install and Release instructions moved to Wiki

closes #252
cffi backend implementation
add Again and ContextTerminated exception subclasses

and _check_rc utility

- [x] makes catching the most common exception cases easier
- [x] breaks nothing
- [x] fixes exception when zmq_poll is interrupted, e.g. terminating IOLoop.

[forcing travis rebuild]
get errno before making any Python calls in _check_rc

why? Because I said so, that's why.

(I have no idea why, but Python 3.2 seems to need it)
test new exceptions

poke @travisbot
tweak gevent bug workarounds

timeout is configurable, and now long (> 10 seconds)
debug message is off by default

ref: #229
Update msg send and recv functions definitions
Add zmq_ctx_new and refactor cffi tests to use

a TestCase instada of test functions
Add linger procedure to context.term()
Fix contexto __del__ and remove unnecessary 

instance method
import constants groups from zmq.sugar
remove socket.rcvmore attribute
use _ to describe private backend attributes
fix cffi zmq_poll implementation
remove cffi duplicated constants grous and import

from sugar in socket.get
remove cffi Poller and unused polling code
Merge pull request #308 from minrk/exceptions

add Again and ContextTerminated exception subclasses
Merge pull request #311 from minrk/greenbarf

tweak gevent bug workarounds

- [x] timeout is configurable, and now long (11.6 seconds, to avoid timeout coincidences)
- [x] debug message is off by default

ref: #229
remove last use of allocate

just use malloc instead