Replace plop with hygen (http://hygen.io).

[jondot]

This tackles a few of the issues that were pointed out with plop and adds lots of scalability for this kind of project (a modular architecture).

Generating a new module now becomes:

$ yarn hygen -- module new --name myNewModule

(see more in docs/ARCHITECTURE.md)

A bit about hygen

• Speed is a first-class concern (and is regularly tested)
• Developer ergonomics are first-class concern
• Scalable - should serve modular projects best, and for multiple teams (not a one big file that's error prone)
• Contextual - can have multiple generators based on where the user is running it from

In terms of features, it has CLI arguments, prompts, smart code injection, and a ton of productivity helpers (dev ergonomics).