added default scope
implemented :call to act as join
implemented open decls
printing of opened modules
a todo note
bugfix: forgot to wrap argument in proc
bugfix in scope.to_s
another solver helper method: compiler
bugfix: forgot a join
change in AType.join: don't return nil if ends are disjoint
implemented <mult>_<mult> methods
extended ExprBuilder to accept products with left multiplicity
minor edits
finished adding all the stuff from the chameleon example