title: Is it possible to Observable.Buffer on something other than time
body: <p>I've been looking for examples on how to use Observable.Buffer in rx but can't find anything more substantial than boiler plate time buffered stuff.</p>
  
  <p>There does seem to be an overload to specify a "bufferClosingSelector" but I can't wrap my mind around it.</p>
  
  <p>What I'm trying to do is create a sequence that buffers by time or by an "accumulation".
  Consider a request stream where every request has some sort of weight to it and I do not want to process more than x accumulated weight at a time, or if not enough has accumulated just give me what has come in the last timeframe(regular Buffer functionality)  </p>