Merge esprint into eslint

[GauthierPLM]

Esprint is the tool that ESlint needed to be usable in a fast development workflow. It speeds up a lot the work.
That why I think it would be an awesome addition to ESlint itself. It would improve the life of many dev and would faster a lot it's daily usage.

It could be available via a --watch option, like what is available for jest.

[lasergoat]

@Kendos-Kenlen have they discussed it on the eslint side?

[GauthierPLM]

Not as far as I know.

[yvele]

Super related to eslint/eslint#3565 (comment)

[bradencanderson]

We'll take direction from the eslint maintainers here. They're totally free to point to a blessed third-party solution or build a first-party one as part of eslint core.

[christianvuerings]

Let's continue this conversation in eslint/eslint#3565 and eslint/rfcs#42