int literals

For now, we don't bother with the rules for untyped
constant expressions, even though these are quite
different from the runtime semantics for numeric values.
binary operators
modify the user's package less

We'd like to minimize the amount of code we put into the
user's package. This change moves the call to interp.Run
out of the injected code into our generated main.
work with non-main packages
print struct field names
removed unused argument