I noticed that once map order no longer depends on the key, the TOML problem #194 is easily solvable by reordering (and without affecting other formats like #221 does). I've added that to this PR.
[Edit:] Using toml 0.6 fixes this issue more cleanly.
Minus one TODO. My first impulse was to reach for indexmap, but
Value::Map
is never actually accessed by key.