1. Add `CHRONIK` log category to BCLog
2. Split `log_println` into `log_print` (logs unconditionally) and `log_print_chronik` (logs to category `BCLog::CHRONIK`)
3. Add `chronik-util` crate
4. Add `log!` (calls `log_print`) and `log_chronik! macro (calls `log_print_chronik`)
Note: There is no (built-in) equivalent to the `__FUNC__` macro in Rust, so we just put `<chronik unknown>` there. Capturing the current function name is possible but requires a bit of a hack (see https://stackoverflow.com/a/40234666).
Note: `__FILE__` in C++ is relative to cwd (e.g. `build`), but `file!()` in Rust is relative to /. We haven't spent any time harmonizing this, as this is sufficient for debugging purposes.