Replace FragmentScanner with scan(), and turn around the bool

[nabijaczleweli]

Take base_dirs: IntoIter<AsRef>, shared_path: AsRef, allowed_extensions: &[AsRef]

This makes client code a hell of a lot more flexible, and the arguments make more semantic sense; in particular, it means you can do

for (filename, filepath) in liboverdrop::scan(["/usr/lib", "/run", "/etc"], "my-crate/config.d", &["toml"], false) {
    println!("fragment '{}' located at '{}'", filename, filepath.display());
}

and it Just Works

[cgwalters]

OK yeah, I'm good with this. I think I'd probably still like a builder-style API potentially but it can be based on top of this later.

However, let's do a semver-compatible release first with the current fixes if that's OK with you?

[nabijaczleweli]

Sure, whatever.

[nabijaczleweli]

This is g2g then I think