5a872880bd
This is my first code contribution to Rust, so I'm sure there are some issues with the changes I've made. I've added the `quote_arg!`, `quote_block!`, `quote_path!`, and `quote_meta_item!` quasiquoting macros. From my experience trying to build AST in compiler plugins, I would like to be able to build any AST piece with a quasiquoting macro (e.g., `quote_struct_field!` or `quote_variant!`) and then use those AST pieces in other quasiquoting macros, but this pull request just adds some of the low-hanging fruit. I'm not sure if these additions are desirable, and I'm sure these macros can be implemented in an external crate if not.