Currently the ast-redux Rust library is required to build kdev-rust. We need an automated way to fetch & build this Rust library for kdev-rust.

Possible solutions:
a) Add ast-redux as an CMake ExternalProject (probably very easy)
b) Add ast-redux as a Git submodule (bigger burden for the developer, since he needs to take care of updating the submodule)

I'de vote for solution (a). Additional, I'd keep a way to be able to use your local build of ast-redux. I.e. by introducing a CMake option in kdev-rust, such as -DAST_REDUX_ROOT=/path/to/ast-redux/target/debug which will disable the ExternalProject build and just the ast-redux library as specified.