One of my fellow forum members was playing with the PCA9555 16 bit IO Expander. The sources he found on the web were always based on accessing the 16 bits at once. He preferred to use the typical pinMode(), digitalRead() and digitalWrite() functions like the Arduino to approach each pin individually. I wrote a library class to support this. As the different types of I2C IO expanders is expanding I will try to make this class as universal as possible. The code can be downloaded from Github.
The code is pretty straight forward. But if someone wishes to make / suggest changes let me know either through a pull request or send me a message through the contact form. This code is open source so you may do with it what you like.