Advanced functionality for working with bookmarks

[GermanAizek]

@totravel, it would be really convenient to work with bookmarks if there were these functions.

/**
    * Compare bookmarks.
    * @param name1 Name first bookmark.
    * @param name2 Name second bookmark.
    * @return enum
    * 0 Bookmarks match.
    * 1 The first bookmark is located below the second one and does not intersect it.
    * 2 The first tab is above the second one and does not intersect it.
    * 3 The first bookmark is located below the second one and crosses it.
    * 4 The first tab is above the second one and crosses it.
    * 5 The first bookmark includes the second one.
    * 6 The second bookmark includes the first one.
    * 7 Bookmarks start in one place, but the first one is longer.
    * 8 Bookmarks start in one place, but the second one is longer.
    * 9 Bookmarks end in one place, but the first one is longer.
    * 10 Bookmarks end in one place, but the second one is longer.
    * 11 Bookmarks are next to each other and the first one is below the second one.
    * 12 Bookmarks are located next to each other and the first one is higher than the second one.
    * 13 One of the bookmarks does not exist.
    */
   int CmpBookmarks(std::string name1, std::string name2);

/**
 * Checking the existence of a bookmark.
 * @param name Name bookmark.
 * @return bool true if bookmark exists, false otherwise.
 */
bool ExistingBookmark(std::string name);