Write display buffer to physical display.

def display(self):
        """Write display buffer to physical display."""
        self.command(SSD1306_COLUMNADDR)
        self.command(0)              # Column start address. (0 = reset)
        self.command(self.width-1)   # Column end address.
        self.command(SSD1306_PAGEADDR)
        self.command(0)              # Page start address. (0 = reset)
        self.command(self._pages-1)  # Page end address.
        for i in range(0, len(self._buffer), 16):
            control = 0x40   # Co = 0, DC = 0
            self._i2c.write_list(control, self._buffer[i:i+16])