Implement Ord for MatchedPath to make its iterator sortable

[yykamei]

It's useful if an iterator of MatchedPath is sortable.

thwack/src/cli.rs

Lines 171 to 175 in 227603e

	// TODO: Sort
	for path in Finder::new(starting_point, query)?.take(limit.into()) {
	let path = path?;
	paths.push(path);
	}

I want to make this comparison algorithm based on positions and relative. Each element of positions is usually adjacent to each other when the specified query is completely included in the MatchedPath (e.g., given query is foo.txt, MatchedPath with src/foo.txt should precede the one with src/components/footer/info.txt). Maybe, the directory depth of the file path might be a factor of sorting. This is the current definition of MatchedPath.

thwack/src/finder.rs

Lines 106 to 110 in 227603e

	pub struct MatchedPath {
	pub absolute: String,
	pub relative: String,
	pub positions: Vec<usize>,
	}