Bug #70569 JSON_VALID allows mixed case in the keyword names

Description:
JSON_VALID treats words null, true, false with mixed case as valid while http://www.ietf.org/rfc/rfc4627.txt?number=4627 clearly says they must be in the lower case.

How to repeat:
mysql> select json_valid('{"a":nuLL}');
+--------------------------+
| json_valid('{"a":nuLL}') |
+--------------------------+
|                        1 |
+--------------------------+
1 row in set (0.00 sec)

mysql> select json_valid('{"a":True}');
+--------------------------+
| json_valid('{"a":True}') |
+--------------------------+
|                        1 |
+--------------------------+
1 row in set (0.00 sec)

mysql> select json_valid('{"a":FaLSE}');
+---------------------------+
| json_valid('{"a":FaLSE}') |
+---------------------------+
|                         1 |
+---------------------------+
1 row in set (0.00 sec)

Fixed in versions 0.2.1 and 0.3.0