Re-encode strings back, so result stays valid JSON

[pashky]

Otherwise any string containing quotes will break resulting JSON

[coveralls]

Coverage remained the same when pulling 6d00440 on pashky:master into a99387e on gongo:master.

[gongo]

Hi @pashky Thanks to PR.

I have converted purposely.
Details: https://gist.github.com/gongo/1789605#comment-962402

If you want to use valid json after reformat, use json-pretty-print-buffer: https://github.com/gongo/json-reformat#important (From Emacs 24.4)

[gongo]

@pashky
If you want merge this PR, Please modify test/json-reformat-test.el

[gongo]

After merge this PR, I think I trying to create the following options:

(setq json-reformat:pretty-print-string t) ;; default nil

If t, result is old style (invalid json) .