a25f9c Add CS10 release notes

Authored and Committed by Carl George 10 days ago
    Add CS10 release notes
    
    As discussed as few times at the promo meetings and in chat, we should
    have proper release notes.  This creates that page and adds a link to it
    (and the existing CS9 release notes) on the downloads page.  It also
    adds a link to it from the header documentation dropdown.
    
        
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