Allow array members delimited by \n inside []

This allows for syntax similar to the modified hash syntax, e.g. (rather
complex example):

    some_array = [
      :foo
      :bar
      [
        'baz'
        :qux
      ]
      {
        :quux => 'grault'
        'garply' => [
          'waldo' => :fred
        ]
        :plugh => 'xyzzy'
      }
    ]