fn runner() and fn from_cli(cli: Cli) util functions are located to
app.rs. However, those are utils for runner. So this commit change the
functions to runner.rs.
This improves the compatibility and adds the ability to introduce
non-breaking changes by using a builder pattern.
Example:
```rust
fn main() {
match xplr::runner(None).and_then(|a| a.run()) {
Ok(Some(out)) => print!("{}", out),
Ok(None) => {}
Err(err) => {
if !err.to_string().is_empty() {
eprintln!("error: {}", err);
};
std::process::exit(1);
}
}
}
```
