#19 media:content Support on item level

[Niko Schmuck]

support for the media:content element at item level for
the RSS 2.0 exporter. The root element looks like
<rss version="2.0"
xmlns:media="http://search.yahoo.com/mrss">
...
</rss>

the test case for parsing

ant test.brief
-Dtestcase=de.nava.informa.parsers.TestRSS_2_0_Parser

(Using the file from test/data/yahoo-topstories.xml)

For the RSS 2.0 exporter the test case can be exec'd with:

ant test.brief
-Dtestcase=de.nava.informa.exporters.TestRSS_2_0_Exporter

(This will produce as side-effect a synthecial newsfeed
in build/test/data/out/export-rss20.xml)