Operator: Sample

[benjchristensen]

http://msdn.microsoft.com/en-us/library/hh211615(v=vs.103).aspx
http://msdn.microsoft.com/en-us/library/hh211892(v=vs.103).aspx
http://msdn.microsoft.com/en-us/library/hh229742(v=vs.103).aspx

[zsxwing]

Still have one overload to do:

public static IObservable<TSource> Sample<TSource, TSample>(
    this IObservable<TSource> source,
    IObservable<TSample> sampler
)

[akarnokd]

I can take this.

[benjchristensen]

Done.