PCF8591 i2c Analog I/O Expander

Library to use i2c pcf8591 IC with arduino and esp8266.
This IC can control (until 4) analog input and/or 1 analog output like measure voltage, read thermistor value or fade a led.
Can read analog value and write analog value with only 2 wire (perfect for ESP-01).
I try to simplify the use of this IC, with a minimal set of operation.