generate StringPtr for Null* enums

add more codegen support for nullables

fix Go struct tag parsing

304ba5d didn't correctly handle struct tags whose
value contained a space. (My fault.)

Use a proper struct tag library with a dedicated parser
that handles all the edge cases. Less code, and better.

fix Go struct tag parsing

304ba5d didn't correctly handle struct tags whose
value contained a space. (My fault.)

Use a proper struct tag library with a dedicated parser
that handles all the edge cases. Less code, and better.

release(cmd/sqlc): Bump to v1.13.0 (sqlc-dev#1523)

* release(cmd/sqlc): Bump version to v1.13.0

* chore: Regenerate test data with latest version

* release: Update download links

* docs: Update the changelog

cmd/sqlc: Bump version to v1.12.0 (sqlc-dev#1415)

* docs: Add v1.12.0 to the Changelog

cmd/sqlc: Bump version to v1.11.0

cmd/sqlc: Bump version to v1.10.0 (sqlc-dev#1165)

cmd/sqlc: Bump version to v1.9.0 (sqlc-dev#1121)

cmd/sqlc: Bump version to v1.9.0-beta1 (sqlc-dev#1103)