This new structure allow us to filter easily Trending shorts and Recently
trending sections.
On the previous one, this Recently trending section is now filtered, by
checking whether sections have a title, which isn't the case for normal trends
contrary to the other ones.
This makes that the extractor returns now only the real 50 "Now" YouTube
trends.
Elements inside arrays are now extracted dynamically instead of only the ones
of the first index, using Java 8's Stream API.
The getInitialPage() method of YoutubeTrendingExtractor can now throw a
ParsingException if no selected tab (corresponding to the one of the trends
type extracted) has been found.
Finally, the licence header has been moved to the top of the file and updated.
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