Add numbers - concatenate strings

---

• Interpolation works on numbers as well
• The + operator is numerical addition or string concatenation

examples/intro/add_numbers.cr

x = 23
y = 19
z = x + y
puts z                     # 42
puts "#{x} + #{y} is #{z}" # 23 + 19 is 42

a = "23"
b = "19"
c = a + b
puts c                     # 2319
puts "#{a} + #{b} is #{c}" # 23 + 19 is 2319