Introduce lerna

[halfzebra]

This is the first PR focused on splitting CEA into separate packages #183

As a first step I'm moving create-elm-app into packages.

[fobos]

Will review it later today

[halfzebra]

@fobos please let me know if you will have time to check this one out!

[fobos]

Am I right that you going to split CEA into separate packages containing simple command for CEA?
Can you describe what are you going to do with it next?

[halfzebra]

@fobos thanks, that's a very good question 🙂

Originally I wanted to move ./scripts/utils into a separate npm package, so ejecting is similar to Create React App, but there's more to it. I have considered rewriting the error overlay in Elm.

I also want to have a reusable elm-app-scripts, which will contain the scripts for running the app, which will enable people to customize Create Elm App with less effort.

Having everything isolated, just as in CRA, there might be an opportunity to create a CRA-compatible elm-app-scripts, so it's possible to use Elm setup with Create React App(not a very big benefit, but might be a low hanging fruit)

I wanted to keep the semantic release setup, but also add lerna to manage a multi-package repo.

[fobos]

Having reusable script is good idea.

[fobos]

@halfzebra thanks for explanation.

[halfzebra]

This is on hold due to atlassian/lerna-semantic-release#89

[halfzebra]

Closing this in favor of adopting https://github.com/Updater/semantic-release-monorepo