Undefined behavior in writeSerialPort() caused by developer error

[iJetColor]

In the Sending Data section of the README, DATA_LENGTH is defined as 255, but the string that is actually passed to writeSerialPort() has a length of 12 characters. If 255 is, indeed, passed as DATA_LENGTH, undefined behavior may occur and can manifest itself as incomplete strings, and some may even be created automatically rather than explicitly defined by the developer.

I propose that writeSerialPort() should find the length of the *buffer string parameter instead of relying on developer input in order to prevent this issue from occurring in the future.