Converted from makefile to tuplua.  I guess there isn't really a need
for a branch for this.
Rewrote script to have a more concise interface, with assertions for
status and more consistent error handling.  Errors are now set by
throwing exceptions.
Fixed some missing returns in new methods.
Fixed IsEmpty debug assertions.
Fixed some error messages and small checks.  Always load libraries.
Print a message even when show errors is off in Script::Do -- hiding error messages doesn't completely make sense.
Added stack element duplicator.  Previously, had one duplicate/move, but now there's separate duplicate and move operations.
Added a sanity check to Do: to make sure nobody's cluttered up the stack before calling.
Separated tests into new repo.