Update to add static NAT translations to the IPv4 address space
See Bug report #971
Additions to patch supplied by Tim Wilkes

Final Credit for the pull request to me

Rebased for 0.20.7 and updated coding style on if statements
Merge pull request #47 from MWilkinson/BUG_971_v2

Feature add - Static Nat Translations for IPv4 - Bug 971 v2