Refactor encoding to use *string instead of string as input

I don't want to clone the whole input string

encoding/gsm7.go

@@ -11,15 +11,15 @@ type GSM7Coder struct{}
 // Otherwise Encode will allocate memory as it sees fit
 // Which is fine but not optimal
 // Preallocate the buffer with the size of EncodesInto bytes
-func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
+func (c *GSM7Coder) Encode(s *string, buf *bytes.Buffer) error {
 	// utf8 := *(*[]byte)(unsafe.Pointer(&s))
-	utf8 := []byte(s)
+	utf8 := []byte(*s)
 	var (
 		offset      int  = 1
 		bitshift    byte = 0
 		leap, shift bool
 	)
-	encodedSize := GSM7EncodesInto(&s)
+	encodedSize := GSM7EncodesInto(s)
 	cap := buf.Cap()
 	if cap < encodedSize {
 		buf.Grow(encodedSize - cap)