Implement a way to utilise tor's logging system from Rust code

We really need a way to use tor's logging subsystem from Rust code. I haven't ever really looked at our logging code because it always Just Works™, but it seems possible that we could construct/format Strings to log in Rust code, choose a logging level, and throw the String across the FFI boundary, have the C code log it, then have the Rust code free it?

I'm not sure what we'll do about logging in general moving forward, once (and if) more and more of tor is rewritten in Rust.