SerialConnection cannot write arbitrary byte sequences

[ryosukecooltanaka]

The write() method of SerialConnection class takes string as an argument and convert them into bytes with the encode() method of the python string (with utf-8), but this can be inconvenient as no strings can be encoded into values between 128~255 (UTF-8 encoding table).

This string encoding can be easily bypassed by directly passing the desired byte sequence to SerialConnection.conn.write(), but conceivably changes can be made such that SerialConnection.write() decides whether or not to encode according to input types.

Not a big deal but just noting here as I wasted 1 hour figuring this out...