A flexible logger that can write to stderr or to log files
See http://emabee.atwebpages.com/rust/flexi_logger/index.html
Add this to your `Cargo.toml`:
```toml
[dependencies]
flexi_logger = "0.5"
log = "*"
```
and this to your crate root:
```rust
extern crate log;
extern crate flexi_logger;
```