minor extensions for VPAID - for more advanced 3rd party interactive content

Hi

my feelings are that you will probably not accept this pull request.. :)

as it deviates from the IAB specs by extending the VPAID 2.0 with a few functions,
needed to provide better integration with more advanced ads.

if it was possible to recommend these updates to IAB it would do more justice,
yet for all practical purposes i tried to change as little as possible,
thus we may call this VPAID 2.1

I will be using this fork within my organization and further implementations
of VPAID.

please advise...

regs