[WIP] Robo 2.x

[greg-1-anderson]

I just released Robo version 1.3.5, which made some improvements to the way dependency injection works that will be important for Robo 2. For now, everything should also continue to work in the original way without any breakage.

Creating a PR to test if that is true here in practice.

[greg-1-anderson]

Well, that didn't work at all. I've reverted the breaking changes in Robo 1.x, and moved them into Robo 2.x development. I'll continue with this PR to see about getting Terminus working with Robo 2, but no pressure to upgrade. Robo 2 will drop support for PHP 5.x; see consolidation/robo#548 for other details.

[greg-1-anderson]

I couldn't get the changes I made in Robo 1.3.5 to work right and still be backwards compatible, so I backed them out in Robo 1.4.0, and moved this work to the Robo 2.x branch. I'll continue to use this PR as a work place to ensure that Terminus remains compatible with Robo 2. We shouldn't merge here until:

• There is a stable release of Robo 2
• Terminus is ready to drop support for PHP 5.6 and earlier, perhaps PHP 7.0 as well (e

Exact supported PHP versions in Robo 2 not decided yet, but 7.0 is EOL. Motivation for dropping 7.0 would be to allow Robo to eventually require dependencies that don't support it, e.g. Symfony 4 -- but it's unclear at this point whether that will be necessary.

Not ready