Funny marks

Here are described marks in Summary mode. Mark is displayed right side of message number as follows:

    1D 07/17 Itojun         v6: items to be no in6_pcbnotify() doesn't
    2o 07/18 Utashiro       Re: behavior after I'm afraid that mark-ring
    38 07/19 Nom-sun        refile info.       Sorry for my late respon

There are four marks at present.

`D'

The mark to delete.

`o'

The mark to refile, that is, to move a message to another folder.

`@'

The mark to process messages at the same time.

`*'

The mark to review.

They are explained step by step.

• delete mark: Delete `D'
• refile mark: Refile `o'
• multi mark: Multiple `@'
• review mark: Review `*'
• unmark: Deleting marks
• mark level: Mark strength