boostbook documentation is at serious risk of becoming impossible to use

I would have opened an "issue" on the boostorg/boostbook project, however, that is not enabled.

I have been duplicating the boostbook setup scripts into the docker setup environment for Ubuntu Bionic and I have found that all of the packages that boostbook depends on are ancient.

| Package | Version | Last Modified | Host |
| --- | --- | --- | --- |
| docbook-xsl | 1.75.2 | 2009 | [SourceForge](http://sourceforge.net/projects/docbook/files/docbook-xsl/1.75.2/docbook-xsl-1.75.2.tar.gz) |
| docbook-xml | 4.2 | 2002 | [oasis-open.org](http://www.oasis-open.org/docbook/xml/4.2/docbook-xml-4.2.zip) |
| fop | 0.94 | 2007 | [Apache](http://archive.apache.org/dist/xmlgraphics/fop/binaries/fop-0.94-bin-jdk1.4.tar.gz) |

These tools are quite old and it is only a matter of time before the older versions could be removed. These external sites are under no particular requirement to keep these older versions of software available. At some point some of these tools may no longer work with current operating system tools, for example fop says that it is for "JDK 1.4".

Each of these tools has a newer version. A project should be initiated to modernize the documentation build to use the latest versions of these tools, or switch to another documentation system perhaps (I saw a discussion on the mailing list).