Make mepo status serial by default

This release changes mepo status to be a serial command by default rather than using multiprocessing. It was found at NAS that mepo status was acting fork-bomb-like spawning many, many processes. This isn't really needed anyway for status in almost any situation.

If users want the old behavior, they can add the --parallel option.

---

From CHANGELOG.md

Changed

• Moved mepo status and mepo restore-state to default to their serial variants rather than parallel by default. At the same time, we remove the --serial option from these commands and add a --parallel option if users want to run them in parallel.

---

What's Changed

• v2: Default status and restore-state to serial by @mathomp4 in #338
• Updated version to 2.3.0 by @pchakraborty in #345

Full Changelog: v2.2.1...v2.3.0