satlog.rs: Simple logger for SAT-like solvers

This outputs logs to stdout as DIMACS comments: c WARN: ... c ERR: ...

For Level::Info messages, the level is not printed: this allows to have a quiet mode for the solver by setting the level filter to LevelFilter::Off.

Example usage

```rust use satlog::SatLogger; use log::LevelFilter;

fn main() { SatLogger::init(LevelFilter::Info); } ```