Use of `[roots]` in `[tokens]` is tricky, because final value of a
`[roots:foo]` will "silently" depend on DESTDIR, while DESTDIR is
only known during install time. On the other hand, `[tokens]` are used only
during build time.
In other words, YOU CANNOT RELY on the value of keys in `[roots]` to be
consistent. For example, consider root:
[roots]
foo = /bar
qux = [ENV:PREFIX]:/quux
`[roots:foo]` will be '/bar' at build time, but "$DESTDIR/bar" at
install time, and `[roots:qux]` will be "$PREFIX/quux" at build time,
but "$DESTDIR/$PREFIX/quux" at install time.
Just about only case when you might want to use it is mentioning it in
a document, when you want the value to be rather "standard" than
"correct", while you still want to respect PREFIX.
So let's not lead new users directly into that rabbit hole.
'newstub' was not so far to being able to update meta-data based on
existing mkit.ini. However, in order to keep the CLI sane, it seems
better to switch to meta-command scheme.