avoid using print() function

This is just a copy of connect_serial() method from brping/device.py (ver 0.1.5)

```py
def connect_serial(self, device_name: str, baudrate: int =115200):
if device_name is None:
print("Device name is required")
return

try:
print("Opening %s at %d bps" % (device_name, baudrate))

## Serial object for device communication
# write_timeout fixes it getting stuck forever atempting to write to
# /dev/ttyAMA0 on Raspberry Pis, this raises an exception instead.
self.iodev = serial.Serial(device_name, baudrate, write_timeout=1.0)
self.iodev.send_break()
time.sleep(0.001)
self.iodev.write("U".encode("ascii"))

except Exception as exception:
raise Exception("Failed to open the given serial port: {0}".format(exception))
```

The request here is:
Kindly avoid using the `print` function in a library like this. If the device name is required, it should be handled as an exception, not with a `print` and `return`:

```py
raise ValueError("Device name is required")
```

And the next `print` is indeed a logging:

```py
logger.info("Opening %s at %d bps", device_name, baudrate)
```

I've had to use workarounds to prevent these `print`s from being sent to my app's stdout:

```py
def brping_muted_print(*args, **kw):
if len(args) == 1:
args = args[0]
log('brping: %s', args)
# brping module uses raw print statements for logging
# with this trick, we turn them into proper logs
brping.device.print = brping_muted_print
```

Thanks

Open brping/device.py and inspect connect_serial(), including the two print calls and the existing exception path. Exercise the missing-device and successful-open cases to confirm that the former raises as described and the latter no longer writes to stdout.

索引モデルが issue の本文から書いたものです。