Allow us to define Bookmark groups: folders/filters which hold pages bookmarked with certain labels.

I press the bookmark button on a page, this marks the page into an "unsorted" or "default" bookmark folder. When I go to look at my bookmarks for this document, I can then sort them into "Reference", "Revisit", "Inspiring", ... and other folders to better sort my dozens of bookmarks for long documents.

Bonus points if I can color code the bookmarks too!