Update API for ZMQ 3.2.0-rc1.
Add support for context options.
Add support for unbind and disconnect.
Upgrade to NuGet 2.0.

- Import libzmq as a solution-level package.
Print zmq version in HelloWorld test.
Update compatibility for libzmq v2.2.0.
Add build script for using a custom libzmq.
Prevent test failures on 2.x build.
Introduce Frame.Empty static getter.
Fix #62: Add ZmqMessage methods from czmq.
Add ehramovich to AUTHORS.
Add SocketOption flags from ZMQ v3.2.x
Add support for some ZMQ 3.2 socket options.
- LastEndpoint. Retrieve the last endpoint set: ZMQ_LAST_ENDPOINT
- RouterBehavior. Set the ROUTER socket behavior: ZMQ_ROUTER_BEHAVIOR
- DelayAttachOnConnect. Manage delay the attachment of a pipe: ZMQ_DELAY_ATTACH_ON_CONNECT
Fix missing file.
Add support for ZMQ 3.2 TCP socket options.
- TcpKeepalive: TCP_KEEPALIVE
- TcpKeepAliveCnt: TCP_KEEPALIVE_CNT
- TcpKeepAliveIdle: TCP_KEEPALIVE_IDLE
- TcpKeepAliveIntvl: TCP_KEEPALIVE_INTVL
* Add support for some ZMQ 3.2 socket options.
- AddTcpAcceptFilter and ClearTcpAcceptFilter: TCP_ACCEPT_FILTER
Documentation tweaks.
Remove 'virtual' from TcpFilter methods.
Update to libzmq.3.3.0-beta1.
Remove getter for RouterBehavior and fix tests.