Reworking tags and transformations, stage 2:
- dependent transformations (ones that depend on cloning history and/or metaproperties) have now the same type Trans.trans and can be registered via Trans, too. - load_driver accumulates appropriate tdecls to be appended to tasks before transformation/printing. At this moment, we have almost everything in place and are ready to remove Register module (subsumed by Trans and Printer in core/) and Prover module (its functions will move to Driver), and convert all printers and transformations to use the new infrastructure. Not implemented yet: - appending driver-imposed tdecls to tasks - when and where? - metas-options - what is the best way to implement them? - syntax/typing for metas in theories and drivers.