Christopher Paolini was 15 when he had an idea. He would write a book, the kind of book that kids like him would want to read. A tale of bravery and battles, friendship and fortitude, dragons and danger. Four books, 2,891 pages and almost 13 years later, he has done that and much, much more. On Tuesday, Paolini’s epic tale of brave farm boy Eragon and his beloved dragon, Saphira, wraps up with the publication of “Inheritance.” Even his most loyal fans are unlikely to get through the 880-page book in one sitting.