Lots of code cleanup

- Try to use iterator adapters and collect in various places, where possible. This especially benefits draw_it.
- Try to use `.map` and other similar methods on Options and Results, where possible
- Replaced nearly all clones with reference-based equivalents
- Summarizing nodes by file extension is now much more efficient
- PartialOrd and PartialEq implementations now agree
- Replace #[cfg(...)] function definitions with simpler if cfg!(...) equivelents
- Simplify CLI Values handling by taking advantage of Values::default
- Various spelling corrections in comments
- Add `ColorState` enum to replace bool, for clarity
- Fix tests that break under some detected terminal widths when paths are long
- Use sort_by instead of (sort, reverse)
- Use new `ExtensionNode` struct internally to simplify extension aggregation code

tests/test_flags.rs

@@ -67,7 +67,7 @@ pub fn test_d_flag_works_and_still_recurses_down() {
     assert!(output.contains("4 ┌─┴ test_dir2"));
 }
 
-// Check against directories and files whos names are substrings of each other
+// Check against directories and files whose names are substrings of each other
 #[test]
 pub fn test_ignore_dir() {
     let output = build_command(vec!["-c", "-X", "dir_substring", "tests/test_dir2/"]);