function to generate a range of IPv4 or IPv6 IP addresses in an array

[RogerHardiman]

This is a re-write of my Pull Request from April 2016
It returns an Array of all the IP addresses between a start and end IP address
Since the April 2016 PR I've made the following changes
a) Fix npm test typo that prevented the CI working
b) Fix linting issues, use let instead of var
c) Add IPv6 support to range function
d) Add npm test for IPv6 support

I use this function in another Open Source project so would be nice to merge it upstream

[RogerHardiman]

This replaces #55 which supported IPv4 and had a typo in the npm test that prevented the CI working