[racket-dev] I'd like to add a sidebar link to all documentation versions in docs.racket-lang.org.

I always have a difficult time looking for the documentation for
previous versions of Racket.  For example, I wanted to compare API
documentation for 5.2.1 vs. the latest.  I visited:

    http://docs.racket-lang.org/

and immediately got stuck.  I had no idea what to do next here.


It turns out that prior versions of documentation are linked from the
"Download" section:

    http://download.racket-lang.org/docs/


Preferably, this link should show up somewhere on the sidebar of the
main documentation site.  I'm proposing:

    https://github.com/dyoo/racket/commit/87a5280b13f7092f730145028fcbdea8a8cc5519


Is this ok?