Add percentile reader

Some things want to specify a percent as a percentile in JSON

Author: ehughsbaird

src/generic_factory.h

@@ -2050,6 +2050,12 @@ class nc_color_reader : public generic_typed_reader<nc_color_reader>
         nc_color get_next( const JsonValue &jv ) const;
 };
 
+struct percentile_reader : public generic_typed_reader<percentile_reader> {
+    double get_next( const JsonValue &jv ) const {
+        return jv.get_float() / 100.0;
+    }
+};
+
 template<typename T>
 static T bound_check( T low, T high, const JsonValue &jv, T read_value )
 {