Rename methods in controller `main`.

The methods (or actions) in main have been renamed, and one has been added. The
result is as follows:

    main#create => main#create_comment
    main#read   => main#read_comment
                => main#read_comment_id

The routing file has been updated to reflect these changes.
Rename controller `main` methods again.

Methods (actions) in controller main have been renamed again.

    main#create_comment => main#create
    main#read_comment => main#read
    main#read_comment_id => main#read_id

The routing file has been updatged again. The plan is to overload `main#create`
to handle both the serving of a form for creating new comment objects, and also
to handle the actual creation of objects.