docs(examples): add example programs

examples/fizzbuzz.lumen

@@ -0,0 +1,13 @@
+// Classic FizzBuzz for the numbers 1 through 15.
+
+for (n in range(1, 16)) {
+    if (n % 15 == 0) {
+        println("FizzBuzz")
+    } else if (n % 3 == 0) {
+        println("Fizz")
+    } else if (n % 5 == 0) {
+        println("Buzz")
+    } else {
+        println(str(n))
+    }
+}