Andy: add keyword-only arguments

Andy: Arbitrary depth copying of arrays.

Andy: Investigate bbox error in uofa-talk Shadowing slide

Andy: change label in coder to a class not an Int

Andy: look at label alignment in rotvenn

Andy: possible optimizations:
    eliminate frame copying in picture.add(picture pic, ...)
    varpush+popcall --> varcall?
    fieldpush+popcall --> fieldcall?
    overloaded::simplify copies
    straight guide which references a subset of a pair vector.
    Is it cheaper to import a bltin module than to call base_venv again?
    varpush+pop --> no op
    varsave+pop --> one op
    closure+pushfunc+varsave+pop --> savefunc
    stack::popWithoutReturningValue
    look at position information saved in program, maybe save separately
    formal::addOps calls trans
    only hash first 3 or 4 args of signature
    rm transToType from varinitArg::trans
    change camp.y to flag arglists with named args

Andy: testing in errortest.asy for packing versus casting, default argument
ambiguities, and whatever else you can think of
    
Andy: operator tuple, to let people define their own tuples

Andy: Decide if we should change vm::error to em in application.cc

John or Andy: Add unit test for AddOps.
