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/tests_symlinks.rs

@@ -39,9 +39,12 @@ pub fn test_soft_sym_link() {
     let a = format!("─┴ {}", dir_s);
 
     let mut cmd = Command::cargo_bin("dust").unwrap();
-    // Mac test runners create long filenames in tmp directories
     let output = cmd
-        .args(["-p", "-c", "-s", "-w 999", dir_s])
+        .arg("-p")
+        .arg("-c")
+        .arg("-s")
+        .args(["-w", "999"])
+        .arg(dir_s)
         .unwrap()
         .stdout;
 
@@ -72,8 +75,13 @@ pub fn test_hard_sym_link() {
     let dirs_output = format!("─┴ {}", dir_s);
 
     let mut cmd = Command::cargo_bin("dust").unwrap();
-    // Mac test runners create long filenames in tmp directories
-    let output = cmd.args(["-p", "-c", "-w 999", dir_s]).unwrap().stdout;
+    let output = cmd
+        .arg("-p")
+        .arg("-c")
+        .args(["-w", "999"])
+        .arg(dir_s)
+        .unwrap()
+        .stdout;
 
     // The link should not appear in the output because multiple inodes are now ordered
     // then filtered.