FYI: major refactor coming

[ndw]

In the course of getting 5.2 ready, I spent a bunch of time cleaning up the build. I've learned a lot about gradle since I started this build.

It'll be a complete refactor of the repo. It's been years since someone expressed an interest in translating it into another language, so I'm taking out the conceit that this is the English version. It's also unlikely that the build system for the 4.x edition survives at all so I'm taking that out.

Along the way, I hope to make new versions of the other docs as well. I'll bring publishers up to be a customization of 5.2 and see if the slides, website, and sdocbook variants can be made reasonable.