Printing to stderr

[D. E. Akers]

The standard error stream is the definitive place to write diagnostic messages that shouldn't be considered part of a program's output. There is, at present, no platform-independent way to write to stderr with lci, and I propose that this should be remedied with due haste. While the specifications are regrettably silent on the matter, several old forum posts suggest‒and many other interpreters use‒an INVISIBLE operator for this purpose. I have taken its popularity into account and submitted a pull request which implements the feature. This post is essentially a request for comments and potentially better names for this keyword.