I experimented and published my own library for the Silicon Labs Si7021 Temperature and Humidity sensor.
The library is for use with the Particle Photon, and fixes some issues I found with the other available ones. For example, it supports the built-in heater, and reading the sensor serial number and firmware revision.
Find it over on my github, or include
it directly via the particle IDE - it is called
Breakout board: Adafruit