Function is_complete_message 

pub fn is_complete_message(buffer: &[u8]) -> Option<&[u8]>

Check a buffer for a message. This method is useful during hardware interrupts, to check whether the received data is a readble message or more data has yet to arrive

Arguments:

• buffer: this argument is NOT for the whole buffer to be passed in but rather the slice of the buffer containing the currently received information

Returns:

• Some: a slice guaranteed to contain a message
• None: a full message hasn’t yet been received