Relation/struct named fields

[Z-snails]

Currently relations only support tuple structs, named field structs would be good for documentation purposes.
I would certainly think it would be useful to use the input structs in non-crepe code, as it could be clearer than anonymous tuples.

[ekzhang]

Hi, thanks for the suggestion. This is possible but also would require quite a few substantial changes to how the compiled code is generated, in particular the index data structure would need to be updated, and more parsing logic for relations introduced.