Make fish-printf no longer depend on the widestring crate, as other clients
won't use it; instead this is an optional feature.
Make format strings a generic type, so that both narrow and wide strings can
serve. This removes a lot of the complexity around converting from narrow to
wide.
Add a README.md to this crate.
This adds a crate containing a new implementation of printf, ported from musl.
This has some advantages:
- locale support is direct instead of being "applied after".
- No dependencies on libc printf. No unsafe code at all.
- No more WideWrite - just uses std::fmt::Write.
- Rounding is handled directly in all cases, instead of relying on Rust and/or
libc.
- No essential dependency on WString.
- Supports %n.
- Implementation is more likely to be correct since it's based on a widely used
printf, instead of a low-traffic Rust crate.
- Significantly faster.
