Restore --tsvlite; add gssub and expand dhms functions

Overview

The primary purpose of this release is to restore --tsvlite which, by its own, would merit a 6.1.1 bugfix release. But since a couple other new features are present as well, this is a 6.2.0 minor release.

All the "Plans for 6.2.0" listed at https://github.com/johnkerl/miller/releases/tag/v6.1.0 are all still in-plan, but since this 6.2.0 exists sooner than later, those issues are planned for a 6.3.0.

Details

PRs:

• Restore --tsvlite by @johnkerl in #984
• Let dhms2sec accept input like "8h" by @johnkerl in #983
• Use fixed OFMT for multi-platform regression-testing by @johnkerl in #988
• Bump github.com/stretchr/testify from 1.7.0 to 1.7.1 by @dependabot in #986
• gssub DSL function by @johnkerl in #989

Full Changelog: v6.1.0...v6.2.0