Document diffJson() options (#332)

* Document diffJson() options

* Tweaks: fix run-on sentences; backtick JSON.stringify; name the JSON.stringify parameter this is similar to

* Add full stop

* Correct docs about how stringifyReplacer & undefinedReplacement interact

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Co-authored-by: Mark Amery <markrobertamery@gmail.com>

README.md

@@ -56,6 +56,10 @@ npm install diff --save
 * `Diff.diffJson(oldObj, newObj[, options])` - diffs two JSON objects, comparing the fields defined on each. The order of fields, etc does not matter in this comparison.
 
     Returns a list of [change objects](#change-objects).
+
+    Options
+    * `stringifyReplacer`: A custom replacer function. Operates similarly to the `replacer` parameter to [`JSON.stringify()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#the_replacer_parameter), but must be a function.
+    *  `undefinedReplacement`: A value to replace `undefined` with. Ignored if a `stringifyReplacer` is provided.
 
 * `Diff.diffArrays(oldArr, newArr[, options])` - diffs two arrays, comparing each item for strict equality (===).