Now it no longer needs to do any unsound type punning. The internal
parameter that the wrapper has access to has been completely type
erased, and only the outer parameter knows about enum T. This also gets
rid of strum and replaces it with a custom trait.
On second thought, this is much better. The resulting file size will be
much smaller because only double quotes need to be escaped. It's also
easier to read at a glance.
This still takes up more space than plain JSON would, but I don't know
if serde_json would allow inlining that JSON. Presumably not. It would
get hairy quickly as a regular embedded JSON string due to the encoding.
