* Fixed/formatted all intradoc links. Various other small doc fixes/typography/etc.
* Clarified semantic similarity with anyhow/eyre types/macros.
* Removed unused MietteError::SetPrinterFailure.
* README now generaed from lib.rs via `cargo readme`.
* More doc fixes, made ErrorHook type public.
* Indentation (docs).
This change removes the bound `T: Clone` in the implementation of
`Source` for `Cow<'_, T>`. This expands the implementation of `Source`
to include types like `Cow<'_, str>`. Importantly, `Cow` always requires
the bound `T: ToOwned` and uses `ToOwned` to implement `Clone` rather
than forwarding to `T::clone`.