Add arrays

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examples/arrays/add.cr

x = [2, 3, 4]
y = [5, 6, 7]
p! x
p! y
z = x + y
p! z

x # => [2, 3, 4]
y # => [5, 6, 7]
z # => [2, 3, 4, 5, 6, 7]