Add VIPGRP functions

[poundy]

Like *AddressGroup, we need *VipGroup functions

[poundy]

I've coded and done some basic tests on a candidate for this. You were right, the core was there from AddressGroup so there wasn't too many things that I needed to grapple with. I'll fix up the document I edited earlier and submit the PR

[poundy]

#89

[alagoutte]

it is now merged and need now to publish a new release.... :)