v1.4.0-beta1

https://github.com/go-reform/reform/milestones/v1.4.0

• Go 1.12+ is now required.
• Converted to Go module. Non modules-aware tools like dep
  are still supported until reform v2 (dependencies with Semantic Import Versioning paths are not used in v1).
• Added context support.
• Added Querier.Count.
  Thanks to Simon Kamenetskiy.
• Added support for github.com/jackc/pgx v3 driver.
• CI now uses GitHub Actions.