Issue #103: allow Infinity and -Infinity to be parsed.

tests/test_parse.expected

@@ -4,6 +4,13 @@ new_obj.to_string()="foo"
 new_obj.to_string()="ABC"
 new_obj.to_string()=null
 new_obj.to_string()=NaN
+new_obj.to_string()=null
+new_obj.to_string()=null
+new_obj.to_string()=null
+new_obj.to_string()=Infinity
+new_obj.to_string()=Infinity
+new_obj.to_string()=-Infinity
+new_obj.to_string()=-Infinity
 new_obj.to_string()=true
 new_obj.to_string()=12
 new_obj.to_string()=12.3