implement optional interface for socket

This provides support for an ipv4 IP address to be provided to address the usecase of listening on specific interfaces and is optional, defaulting to 0.0.0.0.
update readme and example for new option

server.listen updated with changes from a7c859d
fixed addr error when using callback
fix addr value with multiline if
Added support to build on windows

There're minor changes to libssh src to make it build.
Also OpenSSL search path is hardcoded, see
https://github.com/TooTallNate/node-gyp/wiki/Linking-to-OpenSSL and
http://slproweb.com/products/Win32OpenSSL.html
Fix sftp-test failures for recent builds

After digging around for some time, found the fix for the test to pass.
Very likely this is due to ssh2 upgrad.
Merge pull request #37 from jamesallen426/master

Added support to build on windows
Merge pull request #35 from jawsome/bind-interface

Bind interface
Update to work with nan 1.3