Integrate some library functions

It was being included twice, once here and once in library/initialise.jse

It's used to enable code like the following:
${{
  declare_jse("myVar");
  myVar = SomeObjectConstructor();
}}$;

x = myVar.someProperty;

I don't know.  It seemed like magic to me when Nick wrote it at a time when I knew little about JS-EDEN.  But in many circumstances myVar = ${{ SomeObjectConstructor() }}$; would work equally well.  I suppose the choice depends on how often the identifier is going to be needed within the JavaScript part of the construal because root.lookup("myVar").value() does get tedious sometimes.