Updates with core::fmt changes
Updates with core::fmt changes

1. Wherever the `buf` field of a `Formatter` was used, the `Formatter` is used
   instead.
2. The usage of `write_fmt` is minimized as much as possible, the `write!` macro
   is preferred wherever possible.
3. Usage of `fmt::write` is minimized, favoring the `write!` macro instead.

nixpulvis/uuid,tomprogrammer/uuid,mathstuf/rust-uuid,rust-lang-nursery/uuid,rust-lang/uuid