Improve comment layout

[Jesper Öqvist]

Comments in generated code tend to be quite ugly. For example:

    /**
     * 
         * Initializes the child array to the correct size.
         * Initializes List and Opt nta children.
         * @apilevel internal
         * @ast method

     * @ast method
     * 
     */

    public void init$Children() {
    }

The current issues exist with the comments:

• incorrect indentation - parts of the comment may be doubly indented
• duplicate JavaDoc tags (see the @method tag in the above example)
• empty line between the comment and the generated method

[Jesper Öqvist]

Improved documentation comment generation

• generate @declaredat tag for TypeDecls
• don't generate redundant newline after documentation comments
• fixed some incorrect generated comment tags (incorrect @ast method)
• fixed comment indentation issues

fixes issue #142 (bitbucket)

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