remove weird pseudo tabs (\t) and add a prerender flag

1. There are weird pseudo tabs appearing (tested on Windows and Linux)
2. The snapshot file is output as one long line, adding true newlines
3. Also, adding a flag to the body could be useful for the app to know that
this has been pre-rendered (for example, delaying re-loading of templates - see https://github.com/dai-shi/connect-prerenderer for an example)