In `Rules_Tac`, add a `rules_tac` which is `rule_tac` but with the
ability to instantiate the same variable name in multiple theorems.
Also add the specialised `single_instantiate_tac` which allows using the
above mechanism to instantiate a specific variable name in a specific
set of theorems (e.g. "rv" in a set of symbolic-execution lemmas).
Signed-off-by: Rafal Kolanski <rafal.kolanski@proofcraft.systems>
Rafal Kolanski