Fix about_arrays.rb

* Arrays are .class "Array"

* Empty arrays have .size of 0

[#54145629]
Fix about_arrays.rb

* Array.new creates [] empty array

* Literals assign arrays by index
  e.g. array[0] = 1 >> array[1]

* Use of "<<" adds item to end of array

[#54145629]
Fix about_arrays.rb

* Arrays are accessed by index

* Index is zero offset, i.e. 0 = first place

* array[-1] gets last item in array

* .first & .last are special accessors for 0,-1

[#54145629]
Fix about_arrays.rb

* Array[0,1] returns first item at 0 index

* Array[0,2] returns first 2 items starting
  at 0 index

* Asking for items outside of index with a
  positive number gives [], i.e. array[4,100]

* But asking for a 0 item at an index outside
  of range gives nil.  Why?

[#54145629]
Fix about_arrays.rb

* (x..y).to_a range gives x..y in array

* (x…y) gives range x..y-1

[#54145629]
Fix about_arrays.rb

* Ranges can be used to slice arrays

* Beware of zero offset, and neg numbers

[#54145629]
Fix about_arrays.rb

* .push adds item to end of array

* .pop removes item from end of array

[#54145629]
Fix about_arrays.rb

* .unshift(item) adds item to beginning of array

* .shift removes item from beginning of array

[#54145629]