general: apply clippy lints (#407)* general: update crates to 2021 edition. * general: apply clippy --fix * general: apply manual clippy lints * cargo fmt.
Remove needless use of referencesfor further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_mut_passed
Replace `assert!(false, …)`/`assert!(false)` with `panic!(…)`/`panic!()`
implement from and tryfrom string traits for SessionDescription (#348)
Move all to top level