4.0.0 - Library packaging update
The new heater control functionality also caused this library to grow into a collection of files (addition of i2c_bits.py) under a single folder. This major revision update signifies this update. It is sufficient to treat the folder as you would have the file (e.g., add it to your board by copy/pasting into lib folder).
To use in CircuitPython, simply install the Adafruit CircuitPython Bundle.
To use in CPython, pip3 install adafruit-circuitpython-si7021.
Read the docs for info on how to use it.