IPv6 support

[dsamarin]

This incomplete pull request is created to fix #82 and fix #125

Changes

• The Intervals fields are changed to support a 16-byte IP address
• CIDR2Range is updated to support IPv6
• AddRange accepts IPv6 string addresses as well as IPv4
• The requirement of having an interval range that's too large has been removed. This will require discussion, as this may be useful for IPv4 addresses.
• Download IPv4 and IPv6 listings for:
  • Amazon AWS
  • Azure (IPv4)
  • Cloudflare Inc
  • Google App Engine
  • Tor Project (IPv4)
• More efficient implementation of DeleteByName and sort that performs no extra allocation.
• RankBySize uses big.Int to calculate the size of the ranges, as the IPv6 address space is much larger.

In progress

• Assure that generation scripts for C, PHP, and Python will work fine with IPv6 format.
• Assure that lookup class for Ruby also works. (need assistance from a Ruby dev)