Prettify JSON responses

[leo]

By default, we should run them trough JSON.stringify(obj, 0, 2)!

[TooTallNate]

Doesn't this already happen when process.env.NODE_ENV == 'development'?

[leo]

@TooTallNate That's micro - but awesome observation. We need to remove it from there (so that micro is only for prod) and add it to micro-dev by default.

[kandros]

while #58 is a workaround

I tried to patch res.end but it looses the last line for some reasons, can try at https://github.com/kandros/micro-dev/blob/pretty-print-response/lib/pretty-json.js