Add support for ZMQ_IMMEDIATE

Fix bug boolean socket options, when it's impossible to set
a value for a boolean option because sizes of bool and int types
differ on some platforms

Delete tests for router_mandatory and xpub_verbose, because they are not
applicable for subscribe sockets
Merge pull request #27 from xdmiodz/zmq_immediate_support

Add support for ZMQ_IMMEDIATE (Fixes #25)