add rejectDupKeys feature - not yet impld
diff --git a/include/json/reader.h b/include/json/reader.h
index f983ce9..251d7c6 100644
--- a/include/json/reader.h
+++ b/include/json/reader.h
@@ -320,6 +320,8 @@
- `"failIfExtra": false or true`
- If true, `parse()` returns false when extra non-whitespace trails
the JSON value in the input string.
+ - `"rejectDupKeys": false or true`
+ - If true, `parse()` returns false when a key is duplicated within an object.
You can examine 'settings_` yourself
to see the defaults. You can also write and read them just like any