String interpolators for codegens

My work on using string interpolation to write codegen code. For more details see [this pull request](https://github.com/TiarkRompf/virtualization-lms-core/pull/69).

Some recent commits to [TiarkRompf/virtualization-lms-core](https://github.com/TiarkRompf/virtualization-lms-core) are included as well.