Highlight link number for files with multiple links

Curiously enough, this turned out to be helpful today... Git can't
traverse symlinks, so I had to use hard links instead, and then I had to
work out which files had more than one link at a glance. If I hadn't
already had most of exa written, I'd be stuck using find!

colours.rs

@@ -36,7 +36,7 @@ impl Colour {
             Black => "40".to_string(),
             Red => "41".to_string(),
             Green => "42".to_string(),
-            Yellow => "44".to_string(),
+            Yellow => "43".to_string(),
             Blue => "44".to_string(),
             Purple => "45".to_string(),
             Cyan => "46".to_string(),

file.rs

@@ -94,7 +94,15 @@ impl<'a> File<'a> {
             Permissions => self.permissions_string(),
             FileName => self.file_name(),
             FileSize(use_iec) => self.file_size(use_iec),
-            HardLinks => Red.paint(self.stat.unstable.nlink.to_str().as_slice()),
+
+            // A file with multiple links is interesting, but
+            // directories and suchlike can have multiple links all
+            // the time.
+            HardLinks => {
+                let style = if self.stat.kind == io::TypeFile && self.stat.unstable.nlink > 1 { Red.on(Yellow) } else { Red.normal() };
+                style.paint(self.stat.unstable.nlink.to_str().as_slice())
+            },
+
             Inode => Purple.paint(self.stat.unstable.inode.to_str().as_slice()),
             Blocks => {
                 if self.stat.kind == io::TypeFile || self.stat.kind == io::TypeSymlink {