Add some doc comments and factor out add_repeat and add_delimited
Add some doc comments and factor out add_repeat and add_delimited

aidancully/rust,graydon/rust,graydon/rust,rust-lang/rustfmt,SingingTree/rustfmt,aidancully/rust,SingingTree/rustfmt,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,rust-lang/rustfmt,graydon/rust,aidancully/rust