Raw string field value in JSON file

Put simply, no there isn't. Depending on what parser you use, it may have a feature that allows this and/or there may be a variant of JSON that allows this (examples of variants include JSONP and JSON-C, though I'm not aware of one specifically that allows for the features you are looking for), but the JSON standard ubiquitous on the web does not support multiline strings or unescaped special characters.

A workaround for the lack of raw string support in JSON is to Base64 encode your string before adding it to your JSON.