Grow buffer when encoding when necessary

To maybe hopefully prevent multiple allocations

encoding/gsm7.go

@@ -19,6 +19,11 @@ func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 		bitshift    byte = 0
 		leap, shift bool
 	)
+	encodedSize := GSM7EncodesInto(&s)
+	cap := buf.Cap()
+	if cap < encodedSize {
+		buf.Grow(encodedSize-cap)
+	}
 
 	for index, septet := range utf8 {
 		if septet > 0b01111111 {