The WonderSwan Color came out in 2000 and the GBA in 2001, so technically
they're not "video-game consoles of the 1980s and 1990s". Since there's no
elegant way to talk about the 2000-2009 timespan, let's just not mention
dates at all.
Also, some of the text in the higan and icarus settings docs wanted to
link to a discussion of why we ignore manifests by default; now we have
such a thing.
The existing documentation was getting *way* too long to be a single
document.
I've just bulk moved the existing content into the new structure, but it
definitely needs another pass to make the prose match, fix hyperlinks,
etc. etc.