Allow Context to be used as a context manager
Merge pull request #503 from funkybob/context-managers

Make Context a ContextManager
remove link to zmqweb
remove no-longer-required initthreads extension
Merge pull request #505 from minrk/rmweb

remove link to zmqweb
remove unused rebuffer
Merge pull request #506 from minrk/import-init

remove some obsolete Cython files
handle terminated gc context

closes #507
Merge pull request #509 from minrk/gc-teardown

handle terminated gc context
validate ZAP messages

adds checks that ZAP messages are actually valid

Bugs in zeromq (e.g. zeromq/libzmq#948) can result in invalid messages.
These shouldn't result in exceptions in the auth handler.
pass on serial socket example

works on 3.4
Merge pull request #512 from minrk/libzmq-948

validate ZAP messages
Merge pull request #513 from minrk/serialsocket

pass on serial socket example
add travis status to readme
prevent restarting gc during atexit
Merge pull request #516 from minrk/atexit-gc

prevent restarting gc during atexit
fix memory leak in zero-copy allocation

it appears to have been sensitive to
where in the function `malloc` is called.

Calling it later appears to fix the leak.

This is crazy.

Along the way, I cleaned it up to use one malloc of a struct with two ints,
and create the zmq_msg_t in the free_fn,
so if a leak returns it won't be so severe.
Merge pull request #517 from minrk/leaky

fix memory leak in zero-copy allocation
raise ENOTSOCK instead of ENOTSUP on closed sockets

more consistent with underlying libzmq behavior

cffi backend already behaved this way, just change cython to match.
Merge pull request #524 from minrk/enotsock

raise ENOTSOCK instead of ENOTSUP on closed sockets