Implement h-feed-simple tests

[pstuifzand]

• Cleanup the date from the datetime attribute
• Trim the whitespace in the right way

[willnorris]

I'm pretty sure we're already trimming whitespace the right way. From http://microformats.org/wiki/microformats2-parsing#parsing_an_e-_property (emphasis added):

return a dictionary with two keys:

• html: the innerHTML of the element by using the HTML spec: Serializing HTML Fragments algorithm, with leading/trailing whitespace removed.
• value: the textContent of the element after:
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