Noticed that the structs code-generated parsers is no longer committed
when we cut a release, starting with v0.12. We've been committing
generated code to ease reproduction and rebuilding the tag.
Note for example that `structs.generated.go` was present in the [0.11.3
commit](8918fc804a)
but not in the [0.12.1
one](14a6893a25).
We leave the files ignored, so developers don't accidentally commit them
in local development.
