Expression keywords ‘read’ and ‘key’ implemented and tested

Use of StringInput and test of its edge conditions.

Groundwork laid for ‘each’ keyword but no testing.
Dynamic objects, first pass. Does not reuse memory of destroyed objects yet.

The ‘create’ and ‘destroy’ statements haven’t been tested yet either.
Basic object creation by script tested

But have glossed over some subtleties in CreateStatement::make when validating the type identifier.
Will need tests where it is an error to use a non-type identifier.