anchor.diff:  launched, but before the peer listens for incoming segments from other
   peers.
   
  -==== Before segment batch start
  +==== Before batch start
   
   A function that takes two arguments - an event map, and the matching
   lifecycle map. Must return a map that is merged back into the original
   event map. This function is called prior to receiving a batch of
   segments from the reading function.
   
  -==== After read segment batch
  +==== After reading batch of segments
   
   A function that takes two arguments - an event map, and the matching
   lifecycle map. Must return a map that is merged back into the original
  
positive.code:   {})
  
  (defn after-read-batch [event lifecycle]
    (printn "Executing once after this batch has been read.")
    {})
  
  (defn after-batch [event lifecycle]
  
negative.code: has been read by the peer. The segments are available in the event map
  by the key `:onyx.core/batch`.
  
  ==== After apply fn batch
  
  A function that takes two arguments - an event map, and the matching
  lifecycle map. Must return a map that is merged back into the original
  event map. This function is called after the `:onyx/fn` has been applied to the
  input segments and created output segments.
  
  ==== After batch
  
  A function that takes two arguments - an event map, and the matching
  lifecycle map. Must return a map that is merged back into the original
  