rem/data_structures_rb: Sample katas for data structures in Ruby @ 1900ddc0dcb7a03a3a5eaddda56dc3c8932970b2

René Maya ecfdc4dc9e Implement stack using an array		8 lat temu
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single_link_node.rb	c8911ebf8f Update implementation according to tests	8 lat temu
singly_linked_list.rb	f901b25e30 Make singly linked list tests clearer to improve the implementation	8 lat temu
stack.rb	f63f17e922 Implement stack	8 lat temu
stack_using_array.rb	ecfdc4dc9e Implement stack using an array	8 lat temu