== Array#delete_unless

  require 'facets/array/delete'

  a = [1,2,3]
  a.delete_unless{ |e| e == 2 }
  a.assert == [2]

== Array#delete_values

  a = [1,2,3,4]
  a.delete_values(1,2).assert == [1,2]
  a.assert == [3,4]

== Array#delete_values_at

  a = [1,2,3,4]
  a.delete_values_at(1,2).assert == [2,3]
  a.assert == [1,4]
  a = [1,2,3,4]
  a.delete_values_at(0..2).assert == [1,2,3]
  a.assert == [4]

