The Wire documentation only shows read() to get data from
the I²C stream.
However, Wire inherits from Stream, so it gets access to
all the same functions, like readBytes(), which can read
more than one character.
Replace the innermost loop of the cartridge load by
readBytes instead of calling read() in a loop.
The EEPROM in the cartridges support 'Fast I²C' at 400kHz.
Testing it out, it seems to work fine despite the high pull-ups,
so update the Arduino code to enjoy the 4x speed-up !
