Upgrade to Object ownership, membership, lookups, memory safety.  stdlib::object is so unnecessary, the RootNode can just create an appropriate Object now.  ObjectStore does all the actual Object making and ownership now.
getObject/getMember now return non-const everywhere, which we require to do much of anything
Added sketchy implementation of sketchy 'isvar' fake-builtin statement
Implemented shell builtin 'cd', and respect PATH.  Note that standard POSIX path_resolution is largely bypassed/ignored, and in ways that aren't always appropriate.