Add links to TAP14 producer and/or consumers reference implementations

[ligurio]

First of all - thanks for your work with updating specification!

One of the goals of TAP14 is:

Document the observed behavior of widely used TAP implementations.

I believe it would be helpful if authors will link reference implementations to the spec. Testsuites or format linters would be helpful too and will help to make interoperable implementations. may be something like http://instanttap.appspot.com/?