I've generally tried to keep to en_AU spellings rather than en_US spellings
for the sake of my own sanity, but it's difficult when documenting a program
that exclusively uses en_US spellings since I'm quoting the text on
menu-items and in config files.
The file was originally named `higan-config.md` because the dialog box
it described was called "higan Configuration", which was because the
menu-item to open it was in a menu called "Settings" and it would have
been weird to have a "Settings" item in a "Settings" menu.
Now there are individual menu-items for each tab in the Settings dialog,
none of which are named Settings, so the dialog has been renamed back to
"Settings", and the filename should match.
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.