Output ESTree (via a plugin)

[hzoo]

Lots of previous discussions on this:

• babel.transformFromAst doesn't work with ESTree compliant AST babel#2769
• What's the relationship/commitment between the Babel ESTree and Mozilla ESTree? (T6749) babel#3813 (comment) (where I said we would add an option)
• https://github.com/babel/babel-eslint (already does the conversion from babylon to estree+esprima to make babel compatible with eslint)
• https://github.com/babel/acorn-to-esprima - previous extracted logic.

PR is #277

[danez]

react-docgen also wants to upgrade it's parser and being estree compatible would help: reactjs/react-docgen#137