document that cleanup is preparing for Rust 2021
## 0.11.0-dev
- capture errors and count frequency for each, including summary in metrics report; optionally disable with `--no-error-summary`
- - clippy cleanups:
+ - clippy cleanups (prepare for Rust 2021 https://blog.rust-lang.org/inside-rust/2021/03/04/planning-rust-2021.html):
o API change: all `GooseMethod`s renamed to enforce Rust naming conventions in regards to case, for example `GooseMethod::GET` becomes `GooseMethod::Get`
o use `vec![]` macro to avoid unnecessarily pushing data into mutable vectors
o call `format!` macro directly for improved readability
