Forgive me, this is not an issue but a request

[IanKirkEdwards]

Hi Mr. Gerhardt,
I'm a github noob so forgive if this is the incorrect use of "issues". I wanted to ask if you would consider adapting the library to support the PCF8574. I ask because it seems to me that they are currently much more easy to find I/O expander boards. They are available on amazon, mouser and digikey and there are no mcp23017 to be had anywhere I look. Digikey won't be restocking them until at least December. Either way thanks for writing an awesome library! I'll try to adapt it myself but I have a lot to learn!