Structure based API fz_outline is a tree of the outline of a document (also known as table of contents).
title: Title of outline item using UTF-8 encoding. May be NULL if the outline item has no text string.
uri: Destination in the document to be displayed when this outline item is activated. May be an internal or external link, or NULL if the outline item does not have a destination.
page: The page number of an internal link, or -1 for external links or links with no destination.
next: The next outline item at the same level as this outline item. May be NULL if no more outline items exist at this level.
down: The outline items immediate children in the hierarchy. May be NULL if no children exist.
is_open: If zero, the outline element is closed in the UI. If 1, it should be open, showing any child elements.
flags: Bit 0 set -> Bold, Bit 1 set -> Italic. All other bits reserved.
r, g, b: The RGB components of the color of this entry.
