ADD: implements echo program

+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	var input string
+	sc := bufio.NewScanner(os.Stdin)
+	for {
+		fmt.Print("input: ")
+		sc.Scan()
+		input = sc.Text()
+		fmt.Printf("output: %s\n", input)
+	}
+}
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