code: function align(key, leftStream, rightStream, epsilon) {
    // TODO probably need to add stream options support for thigns like high water mark
    var aligner = new Aligner(key, {}, epsilon)
  
    var l = left()
    var r = right()
  
    var ended = 0
    l.on("end", function () {
      l.unpipe(aligner)
      if (++ended == 2) aligner.end()
    })
    r.on("end", function () {
      r.unpipe(aligner)
      if (++ended == 2) aligner.end()
    })
  
    leftStream.pipe(l).pipe(aligner, {end: false})
    rightStream.pipe(r).pipe(aligner, {end: false})
  
    return aligner
  }
docs: align takes two objectMode streams and a sequence key and will create a stream
  aligning records from each stream resulting in a stream that emits record doublets
  when the sequence key exactly matches. IMPORTANT: This only works on ordered streams!
  @param  {String} key The sequence key the two streams are storted by and will be joined by.
  @param  {Stream} leftStream  An objectMode stream ordered by `key`
  @param  {Stream} rightStream An objectMode stream ordered by `key`
  @return {Stream}             A doublet stream containing [leftRecord, rightRecord], [leftRecord, null], or [null, rightRecord]