macro_railroad per Lukas Lueg

Display syntax-diagrams for Rust-macros on docs.rs and doc.rust-lang.org

Using the `macro_railroad`-library this extension generates syntax diagrams for all macros documented on docs.rs. The diagrams are display beneath each macro-block.

Use the icons in the lower right corner to control options and expand the diagram to fullscreen.

This extension is open source, contributions are very welcome: https://github.com/lukaslueg/macro_railroad_ext