_pixelbuf` was renamed to `adafruit_pixelbuf` in CircuitPython 7.0. `adafruit_pypixelbuf` has been migrated to `adafruit_pixelbuf`. This library will maintain backwards compatibility with `_pixelbuf` and `adafruit_pypixelbuf` until such time as it is no longer necessary.
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-neopixel`.
Read the [docs](http://circuitpython.readthedocs.io/projects/neopixel/en/latest/) for info on how to use it.