Formatter doesn't handle CASE expressions and statements

Formatter doesn't handle CASE expressions and CASE statements.

Related to #272.

Examples:

CASE expression:

-- original
SELECT CASE 1
    WHEN 1 THEN
        'one'
    WHEN 2 THEN
        'two'
    ELSE
        'more'
END;

-- formatted
SELECT CASE
    1 WHEN 1 THEN 'one' WHEN 2 THEN 'two' ELSE 'more'
END;

CASE statement:

-- original
CREATE PROCEDURE p()
BEGIN
    DECLARE
        v INT DEFAULT 1;
    CASE v
        WHEN 2 THEN
            SELECT v;
        WHEN 3 THEN
            SELECT 0;
        ELSE
            BEGIN
            END;
    END CASE;
END;

-- formatted
CREATE PROCEDURE p()
BEGIN
    DECLARE
        v INT DEFAULT 1; CASE v WHEN 2 THEN
    SELECT
        v; WHEN 3 THEN
    SELECT
        0; ELSE
    BEGIN
        END
            ;
    END CASE;
END;

将 MySQL CASE 表达式和 CASE 语句的参考资料，以及两个格式化示例作为验收用例。将当前 formatter 的行为与相关 issue #272 进行比较，然后找到 formatter 的入口点，并为两种形式补充覆盖；完成的标准是每个示例都保留可读的 CASE 和语句子句缩进。