Getters and setters


In the interest of convenience, I've added getter/setter methods that wrap the type-specific `{Get,Set}SockOpt*` methods. 

Following the conventions in [Effective Go](http://golang.org/doc/effective_go.html) the setters are named with a 'Set' prefix (ex. `SetLinger`) and the getters are just plain (ex. `Linger`).