Fixes: https://github.com/zkat/miette/issues/176
Change the default ansi color theme to use colors that are more similar
to the colors from the default RGB theme. In particular, don't use red
for any of the span labels, since that color is also used for errors.
BREAKING CHANGES:
* the default theme now prefers ANSI colors, even if RGB is supported
* `MietteHandlerOpts::ansi_colors` is removed
* `MietteHandlerOpts::rgb_color` now takes an enum that controls the
color format used when color support is enabled, and has no effect
otherwise.
* 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).
George Pollard
Nathan Whitaker
Luca Palmieri
Benjamin Lee
Rain
Christopher Durham
Moritz Mœller
Kat Marchán
Kirill Vasiltsov