Array::eachPair A useful method for interacting each element of an array with another (#32)

I’ve got this classic n2 collision detection code and I wanted to separate out all the iteration business into its own place. So I spent a long time trying to figure out the name for the method, searching around in case anyone had anything similar. I finally found it each_pair, which is exactly what I wanted. The each implies iteration, and we are iterating over each possible pair of items from the array.

###*
Call the given iterator once for each pair of objects in the array.
 
Ex. [1, 2, 3, 4].eachPair (a, b) ->
  # 1, 2
  # 1, 3
  # 1, 4
  # 2, 3
  # 2, 4
  # 3, 4 
 
@name eachPair
@methodOf Array#
@param {Function} iterator Function to be called once for 
each pair of elements in the array.
@param {Object} [context] Optional context parameter to be 
used as `this` when calling the iterator function.
###
Array::eachPair = (iterator, context) ->
  length = this.length
  i = 0
  while i < length
    a = this[i]
    j = i + 1
    i += 1
 
    while j < length
      b = this[j]
      j += 1
 
      iterator.call context, a, b

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