ArduinoISP.ino does not properly handle word-based address for EEPROM read/write

**Steps to reproduce**
Reading and writing EEPROM using Adafruit ArduinoISP.ino will cause Bad EEPROM data. The official Arduino [ArduinoISP.ino](https://github.com/arduino/arduino-examples/tree/main/examples/11.ArduinoISP/ArduinoISP) does not have similar issue. See avrdudes/avrdude/issues/990
 
**Possible solution**
The read and write EEPROM function does not handle word-based address. The high address byte is 0x00 in both function. 
https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/0090edd636158f91e5356d7806f3f21cea0c9cde/ArduinoISP/ArduinoISP/ArduinoISP.ino#L550-L557
https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/0090edd636158f91e5356d7806f3f21cea0c9cde/ArduinoISP/ArduinoISP/ArduinoISP.ino#L487-L496



	char eeprom_read_page(int length) {
	// here again we have a word address
	for (int x = 0; x < length; x++) {
	byte ee = spi_transaction(0xA0, 0x00, _addr*2+x, 0xFF);
	Serial.write( ee);
	}
	return STK_OK;
	}

	byte write_eeprom(int length) {
	// here is a word address, so we use here*2
	// this writes byte-by-byte,
	// page writing may be faster (4 bytes at a time)
	for (int x = 0; x < length; x++) {
	spi_transaction(0xC0, 0x00, _addr*2+x, buff[x]);
	delay(45);
	}
	return STK_OK;
	}

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ArduinoISP.ino does not properly handle word-based address for EEPROM read/write #2186

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ArduinoISP.ino does not properly handle word-based address for EEPROM read/write #2186

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