Both normalize_doc_attributes and wrap_comments require an unstable toolchain

[ghost]

The formatting options used by the cargo install version (https://github.com/oxidecomputer/progenitor/blob/main/cargo-progenitor/src/main.rs#L94) use formatting options that are documented as unstable:

• https://rust-lang.github.io/rustfmt/?version=v1.7.1&search=#normalize_comments
• https://rust-lang.github.io/rustfmt/?version=v1.7.1&search=#wrap_comments

RUST_BACKTRACE=1 cargo progenitor -i api-definition.yml -o output -n output -v 0.1.0
-----------------------------------------------------
 TYPE SPACE
-----------------------------------------------------
....
-----------------------------------------------------

thread 'main' panicked at /Users/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-progenitor-0.7.0/src/main.rs:101:68:
called `Result::unwrap()` on an `Err` value: Unstable("wrap_comments, normalize_doc_attributes")
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: cargo_progenitor::reformat_code
   4: cargo_progenitor::main

[ahl]

Yeah: I'm pretty unhappy with the choice I made here... and with the options available. I'd like to use rustfmt for formatting so that the generated code could pastt cargo fmt... but it's not feasible to use it as a library and shelling out has many problems--including the one you've noted. At this point, I'm inclined to switch everything over to prettyplease and see if that's a better experience. PRs welcome or I'll try to get to it in the next week or two.