Ncc: Add flow type support

[gabrielperales]

TypeScript is winning popularity, but I we are a lot of people who still using flow.

[rauchg]

I think one way that we could accomplish this is with optional .babelrc support, provided that adding the optional babel support doesn't increase our bundle too much or make us slower to boot.

If you are interested in working on that @gabrielperales, please let me know.

[zuohuadong]

now， facebook use typescript ~~