cargo-clippy tells us that the `crate::helpers::json::to_writer` and
`crate::helpers::toml::to_writer` functions were implemented without
checking the return value of the `write()` function called inside.
That might lead to serious issues on the user site, if indeed not all
bytes were written.
This patch fixes the issue of the user not knowning about the issue by
introducing a new error variant and returning it in case of unfinished
writes.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Matthias Beyer
D. Scott Boggs