Add goldenfile (testing library)

A library for doing goldenfile testing (testing by comparing test-generated files to older files)

README.md

@@ -635,6 +635,7 @@ See also [Are we (I)DE yet?](https://areweideyet.com/) and [Rust Tools](https://
 * [tarpaulin](https://crates.io/crates/cargo-tarpaulin) — A code coverage tool designed for Rust [<img src="https://api.travis-ci.org/repositories/xd009642/tarpaulin.svg?branch=master">](https://travis-ci.org/xd009642/tarpaulin)
 * [trust](https://github.com/japaric/trust) — A Travis CI and AppVeyor template to test your Rust crate on 5 architectures and publish binary releases of it for Linux, macOS and Windows
 * [fake-rs](https://github.com/cksac/fake-rs) —  A library for generating fake data [<img src="https://api.travis-ci.org/repositories/cksac/fake-rs.svg?branch=master">](https://travis-ci.org/cksac/fake-rs)
+* [goldenfile](https://github.com/calder/rust-goldenfile) - A library providing a simple API for goldenfile testing. [<img src="https://travis-ci.org/calder/rust-goldenfile.svg?branch=master">](https://travis-ci.org/calder/rust-goldenfile)
 
 ### Transpiling