Contents:
Added IPArray.mask() to apply net and host masks to an array of IP addresses (GH#36).
IPArray.mask()
Added ip_range() for generating an array of regularly-spaced IP addresses (GH#27).
ip_range()
Added IPArray.netmask() and IPArray.hostmask() (GH#30).
IPArray.netmask()
IPArray.hostmask()
Fixed Python 2 dependencies so that the ipaddress backport is installed automatically when install cyberpandas from PyPI (GH#29).