21cmFAST v3: A Python-integrated C code forgenerating 3D realizations of
  the cosmic 21cm signal
  This brief code paper presents a new Python-wrapped version of the popular
21cm cosmology simulator, 21cmFAST. The new version, v3+, maintains the same
core functionality of previous versions of 21cmFAST, but features a simple and
intuitive interface, and a great deal more flexibility. This evolution
represents the work of a formalized collaboration, and the new version,
available publicly on GitHub, provides a single point-of-reference for all
future upgrades and community-added features. In this paper, we describe simple
usage of 21cmFAST, some of its new features, and provide a simple performance
benchmark.
