migrate_plus splits up

For anyone currently using the migrate_tools (drush and UI tools for managing migrations) or migrate_source_csv (CSV source plugin) submodules of migrate_plus with their Drupal 8 migration projects, a heads-up - they're being split off into separate projects.

What's happening

New projects have been created for migrate_tools and migrate_source_csv. The plan is to create real (beta or RC) releases for these projects by next Monday, November 16. On that day, a release of migrate_plus will be cut that no longer contains those two modules.

What do I do about it?

If you try to install the new projects today alongside the main branch (8.x-1.x) of migrate_plus, you'll have conflicts. If next week you install that upcoming release or later of migrate_plus without also installing migrate_tools and/or migrate_source_csv, you're gonna have a bad time. So, you need to coordinate. Either:

1. On or after November 16, when upgrading migrate_plus be sure to simultaneously install migrate_tools and/or migrate_source_csv.
2. If you'd like to get ahead of the game, you can install the "split" branch of migrate_plus along with migrate_tools/migrate_source_csv. You can then later upgrade migrate_plus at will.

Why move things around?

1. It's confusing to have the migrate_plus project be a grab-bag of random migrate-related stuff, including a migrate_plus module.
2. Separate modules allows for different maintainers for different pieces of the migration ecosystem. In particular, the monolithic D7 Migrate module has had a single active maintainer (me) for most of its life - breaking things out into smaller bits will help spread out the maintenance responsibility. For one thing, a relatively constrained source plugin module would be a better fit for a relative novice contributor compared to a full toolkit.
3. The test framework does not handle submodules well. This already bit migrate_source_csv.

Speaking of source plugins...

There is an XML source plugin now - I haven't vetted it myself yet, but will be working with it in the coming weeks. And, there is also a brand-new JSON source plugin. The ecosystem is filling in some need niches!