revised Java->Scheme docs

I've fixed some typos in the revised Java->Scheme interface docs, but
there are still some problems that need fixing:

1)

Saying that one needs an AppContext, heap and Interpreter to call into
Scheme is not quite accurate. One needs
a) a heap
b) an AppContext
c) a DynamicEnvironment
d) an Interpeter

It is important that we do not forget to mention the DynamicEnvironment.

A diagram would help to illustrate the relationships. See the attachment
for what I came up with.



2)

We need to document Context.execute(DynamicEnvironment, SchemeCaller),
and Context.enter(DynamicEnvironment).


3)

We need to document how to define and get hold of bindings,
i.e. Interpreter.define and Interpreter.lookup.



Matthias