rust-chg: add project skeleton This directory will host the reimplementation of cHg in Rust. It will use Tokio [1], and tokio-hglib [2] which I wrote for an oxidized CHg, no idea if there's such carbon bonding in nature btw. [1]: https://tokio.rs/ [2]: https://bitbucket.org/yuja/tokio-hglib/ The reasoning for depending on Tokio is that it will allow us to handle Unix signals in a safer way. Well, I believed that until I found a weird function, handlestopsignal(), in cHg codebase. It resends the same signal to the same process by temporarily masking the handler, which can't be inherently async. So the signal handlers will stay in C, which means there isn't actually much reason to write async code right now, other than I've already done most of the async stuff, and slightly easier pager handling. The reasoning for the rewrite is that it will eventually be possible to port server-side config validation back to the client side, which will reduce the complexity of the current daemon management. It will also encourage us to write frontend library (e.g. command line and config parsers) in Rust. The license is GPL2+ because it's likely to include derived work from the cHg of C. The rust/chg crate is excluded from the root workspace as it's unclear how the whole rust packages should be laid out. That can be revisited later.