vast4 0.1.0

An implementation of VAST 4.2 FINAL.
Documentation
<VAST version="4.2" xmlns="http://www.iab.com/VAST">
  <Ad id="20010" sequence="1">
    <Wrapper followAdditionalWrappers="0" allowMultipleAds="1" fallbackOnNoAd="0">
      <AdSystem version="4.0">iabtechlab</AdSystem>
      <Error><![CDATA[https://example.com/error]]></Error>
      <Impression id="Impression-ID"><![CDATA[https://example.com/track/impression]]></Impression>
      <ViewableImpression id="1543">
        <Viewable><![CDATA[https://search.iabtechlab.com/error?errcode=102&imprid=s5-ea2f7f298e28c0c98374491aec3dfeb1&ts=1243]]></Viewable>
        <NotViewable><![CDATA[https://search.iabtechlab.com/error?errcode=102&imprid=s5-ea2f7f298e28c0c98374491aec3dfeb1&ts=1243]]></NotViewable>
        <ViewUndetermined><![CDATA[https://search.iabtechlab.com/error?errcode=102&imprid=s5-ea2f7f298e28c0c98374491aec3dfeb1&ts=1243]]></ViewUndetermined>
      </ViewableImpression>
      <Creatives>
        <Creative id="5480" sequence="1" adId="2447226">
          <Linear>
            <TrackingEvents>
              <Tracking event="start"><![CDATA[http://example.com/tracking/start]]></Tracking>
              <Tracking event="progress" offset="00:00:10"><![CDATA[http://example.com/tracking/progress-10]]></Tracking>
            </TrackingEvents>
          </Linear>
        </Creative>
      </Creatives>
      <VASTAdTagURI><![CDATA[https://raw.githubusercontent.com/InteractiveAdvertisingBureau/VAST_Samples/master/VAST%204.0%20Samples/Inline_Companion_Tag-test.xml]]></VASTAdTagURI>
    </Wrapper>
  </Ad>
</VAST>