* Use hash of ADT name and constructor idx to generate tag, add reverse mapping to module and use where appropriate
* Lint and build fixes
* Add round-tripping test for getting constructors by tag
* Use int64_t everywhere for tags
* Add additional identity check
* Bring out _arg_to_ast again
* Use 8-bit hash of GTV name as MSB of tag, index as LSB for more readable tags
* Use int32 instead of int64 for tag
