Implement API socket operations

Hi @fagg ,

This is a work on the top of pull request #10 , here I've implemented the remaining part of main socket operations: `zmq_close`, `zmq_bind`, `zmq_unbind` and `zmq_disconnect`.

Tests were implemented and are passing under `Windows + Matlab` and `Ubuntu + Octave`.

As I've started the work before your clarifications about the coding style, maybe it is not 100% consistent, but I've done a _best effort_ attempt, with lot's of rebase and rewriting.

Please let me know if any update is necessary.