Close unclosed files (#735)

* Cose unclosed files

* Close additional unclosed file

* Dont use defer in loop

* Removed missed instances of defer in loop

eBook/examples/chapter_12/read_files.go

@@ -24,5 +24,6 @@ func main() {
 		for line, _, err := r.ReadLine(); err != io.EOF; line, _, err = r.ReadLine() {
 			fmt.Printf("Lines: %v (error %v)\n", string(line), err)
 		}
+		fin.Close()
 	}
 }