Adds support for the VASTAdTagURL-Tag

This tag was part of an older version of the VAST2.0 standard (when it was still in draft, presumably), but it is used on some systems out there. It was replaced by the already supported VASTAdTagURI-Tag. For more information see here: http://support.brightcove.com/en/video-cloud/docs/vast-wrapper-ads
trim() the node-content

Older browsers (we saw it happening with older versions of IE) in combination with wierd ad-servers would include empty spaces before and/or after a node's text-value. This fix will trim the textContent, thus removing leading and trailing spaces.
Added testcase
Merge pull request #62 from simpleTechs/support-vastadtagurl

Add support for the VASTAdTagURL-Tag
Merge pull request #63 from simpleTechs/fix-spaces-in-nodetext

trim() the node-content