[plt-dev] `rico' and ".rkt"

I agree.  I simply don't see the point to moving past the three-letter
suffix space.

For what it's worth, .rck and .rkt don't seem to mean much (Google for
"<ext> file extension"), other than this:

http://www.econsultant.com/file-extensions-r/rkt-file-extension-rocksim-rocket-design-file.html

which is a niche we don't really clash with.

Shriram