This restores all stuff removed in previous commit, except one thing:

    // Message options
    MORE = MessageOption(C.ZMQ_MORE)

Handling of SocketOptions has changed, because the type of some options
has changed in ZeroMQ 3. The package should now work with these options
for all versions of ZeroMQ (2.1, 2.2, 3). It compiles, and the tests run
without error, but there should be tests included specific for setting
and getting socket options.

This also fixes one bug, possibly two:

* RCVHWM was defined with C.ZMQ_SNDHWM instead of C.ZMQ_RCVHWM

* GetSockOptBool() now uses an int for the call to C, and converts is to
  bool afterwards.