[boost] [Boost.Book] How to go full-bleed on documentation image headers?

Subject: [boost] [Boost.Book] How to go full-bleed on documentation image headers?
From: Vinnie Falco (vinnie.falco_at_[hidden])
Date: 2016-08-26 10:16:04

On the Boost website, the image in documentation headers is full bleed
(no white border). For example:
http://www.boost.org/doc/libs/1_61_0/doc/html/boost_asio.html

How do I achieve this in my own documentation? I have set the image in
the Jamfile, but I have no idea how to adjust the border:
http://vinniefalco.github.io/beast/index.html

The Jamfile and supporting source files are here:
https://github.com/vinniefalco/Beast/tree/master/doc

Thanks