Unexpected behaviour of print(char, HEX) and print(int, HEX)

```
char c = 255;
Serial.print(c, HEX);
```

produces

```
FFFFFFFF
```

This is due to the fact that `print(char c, int base)` convert char c (1 byte) into an unsigned long (4 bytes). As char is signed 255 is in fact -1(Two's complement), once written in 4 bytes it becomes FFFFFFFF. But as a user I would rather have FF than FFFFFFFF.

The problem exist with int (2 bytes) too

Here is a more complete example:

```
void setup() {
Serial.begin(9600);
int i = 1;
Serial.print("i: ");
Serial.print(i, 10);
Serial.print(" | ");
Serial.println(i, HEX);
i = -1;
Serial.print("i: ");
Serial.print(i, 10);
Serial.print(" | ");
Serial.println(i, HEX);

char c = 127;
Serial.print("c: ");
Serial.print(c, 10);
Serial.print(" | ");
Serial.println(c, HEX);
c = 255;
Serial.print("c: ");
Serial.print(c, 10);
Serial.print(" | ");
Serial.println(c, HEX);
}

void loop() {}
```

output

```
i: 1 | 1
i: -1 | FFFFFFFF
c: 127 | 7F
c: -1 | FFFFFFFF
```

where I owuld rather have

```
i: 1 | 1
i: -1 | FFFF
c: 127 | 7F
c: -1 | FF
```

首先定位 issue 中描述的 Serial.print(char c, int base) 和 Serial.print(int, int base) 重载，然后运行完整的示例 sketch 以复现输出。当十六进制输出使用操作数的宽度，对作为 int 的 -1 产生 FFFF、对作为 char 的 -1 产生 FF，同时保留现有的十进制输出时，即表示完成。

由索引模型根据 Issue 内容生成。