Encoding and decoding of `settings::Settings` now handled in macros to
avoid code repetition. I also wish rewrite them both in a combined
macro that would either encode or decode the struct depending on how
it was called.
Replaced some log warnings with errors
Now if type extension is not valid, the code will still attempt to
decode it, first as JSON data, then as Yaml data. If both fail, then
an error is returned. For this, I added the Display trait to the
`settings::Settings` struct which allows the FromStr trait, and due
to conflicting implementation, I removed the From trait and
implemented manually the `from` method with the same signature -- the
struct just lacks the trait that comes with it.
Replaced lots of warns by errors
Filetype detection won’t return an error on unknown extension anymore,
but will return an `Other` value so it can be handled by other
functions not as an error already. See upcoming commits.
`write_file` now accepts as its second argument any type that
implements the `ToString` trait so that not only Strings will be
accepted but any type that can be turned into one.
