Parser Error Details by Zed Lopez

This offers ``showcommand``, which beefs up version of the testing command ``showverb``, chiefly by listing all of the equivalent verbs for a given verb.

It has no dependency on ShowVerbSub or any testing routines, so it could be compiled for release.

The use option:

``` Use show commands after parser error. ```

makes it automatically invoke after parser errors.

This is offered as a running version of Andrew and Aaron's decade-old proofs of concept. ``showcommand`` may be useful to authors during development, but I don't conceive of this as something anyone would want to drop as is into a game for release.