Simple error handling and highlighting for source files.
```rust let mut src = Source::new("my-file.txt", "The quick brown fox...");
src.addmessage(0..0, "All of my problems start here."); src.addmessage(4..8, "Turns out this isn't quick."); src.add_message(16..18, "And it's not a fox!");
// Pretty print the messages: println!("{}", src); ```
```
my-file.txt:1:1
my-file.txt:1:5
my-file.txt:1:17
1 │ The quick brown fox... │ │ ├───┘ │ │ │ │ │ ├─┘ │ 1 2 3 │ ```