the tiddler gets transcluded in the stylesheets like so:
```
font-family: {{$:/themes/tiddlywiki/vanilla/settings/fontfamily}};
```
note - the semicolon at the end
So this semicolon is superfluous
The trouble with the previous approach of storing several settings in a
single data tiddler was that it made it hard to introduce new settings.
Users who already have a custom copy of the settings/metrics tiddler
wouldn’t get the default settings. The new approach uses individual
tiddlers for each setting.
This commit also introduces a new theme tweak for the cutoff width for
switching between responsive views.
