Auto merge of #291 - kamalmarhubi:newtype-convention, r=@posborne
Auto merge of #291 - kamalmarhubi:newtype-convention, r=@posborne

conventions: Codify use of newtypes

MarkusJais/nix-rust,kamalmarhubi/nix-rust,kamalmarhubi/nix-rust,MarkusJais/nix-rust,xd009642/nix,nikklassen/nix-rust,berkowski/nix,Susurrus/nix,nix-rust/nix,geofft/nix-rust,kamalmarhubi/nix-rust,asomers/nix,xd009642/nix,MarkusJais/nix-rust,carllerche/nix-rust,berkowski/nix,carllerche/nix-rust,xd009642/nix,geofft/nix-rust,asomers/nix,Susurrus/nix,posborne/rust-nix,posborne/rust-nix,Susurrus/nix,nix-rust/nix,carllerche/nix-rust,posborne/rust-nix,nikklassen/nix-rust,geofft/nix-rust,nikklassen/nix-rust,berkowski/nix