Add translator variable for news posts?

**Not for merging**, only for tests and as basis for discussion.

There might be a need for a `translator` variable in news posts, to give credits to the contributors that translate posts, see #145. I personally don't care, but why not, since it's easy to implement.

I added the information in one of the recent posts (Ruby 1.9.3-p429), with translations for `de` and `fr`. @chikamichi I didn't provide a french translation for "translation" on purpose, to test the defaulting to en :) If provided, the translator is printed below the author line at the bottom of the post, like

    Posted by usa on 14 May 2013
    Translation: John Doe

What do you think?