Extends tags report in order to mix request and timer tags

[johnnoone]

I would be useful to mix request and timers tags into tags report.

For this purpose, COMMENT parsing would be upgraded in order to distinguish request tags from the legacy ones.

I suggest to prepend the request tag by a "~" character.
For example, I need to mesure "foo" and "bar", and my request sends these data:

  request:
    tags: foo
    timer:
      - tags: bar

Then the table definition would be:

  CREATE TABLE `tag_info_foo_bar` (
    `foo_value` varchar(64) DEFAULT NULL,
    `bar_value` varchar(64) DEFAULT NULL,
    `req_count` int(11) DEFAULT NULL,
    `req_per_sec` float DEFAULT NULL,
    `hit_count` int(11) DEFAULT NULL,
    `hit_per_sec` float DEFAULT NULL,
    `total_time` float DEFAULT NULL,
    `median_time` float DEFAULT NULL,
    `ru_utime_value` float DEFAULT NULL,
    `ru_stime_value` float DEFAULT NULL,
    `index_value` VARCHAR(256) DEFAULT NULL
  ) ENGINE=PINBA DEFAULT CHARSET=latin1 COMMENT='tag_info:~foo,bar'

where ~foo is the name of the request tag foo, and bar is the name of the timer tag bar.