ESP32 support

[bfaliszek]

No description provided.

[maarten-pennings]

Hi, first time for me to work with the merge request tool, so be gentle with me :-)
I appreciate that you add support for ESP32, but I do have some doubts:

• My style was to have one line of comment describing the hardware setup, and then (one line of) code for that setup. There were only two setups: ESP8266 and Nano. And the user has to use comments to select what he wants. This style is now broken. ESP8266 and ESP are automatically selected due the the #if's, but the Nano isn't. And the comment for the ESP is missing. This is inconsistent.

• My drive for the examples is that they have to be easy (to understand), so short. The libs can be hard. Adding the #if's doesn't make it easy. On the other hand, the flash example is not really an example so we could go for not-easy-but-working-out-of-the-box. In that case, we would need #if's for e.g. Nano (and maybe others).

• I was also looking at the other examples; they are really examples (so I want to "keep it simple"), so should this one be different?

[bfaliszek]

I use your library with ESP32 and it works without a problem. The only difference compared to ESP8266 is the ability to define i2c pins. I have 4 different ESP32 boards and each has different pins, so I thought that the possibility of defining them would be very useful. In addition, I tested this firmware upload from ESP32 on... 125 CCS811 :D

When it comes to merge request or code formatting, you don't have to use my code at all. I just wanted to let you know that you can flash CCS811 with ESP32 and define any pin for i2c. It doesn't require any major code changes.