docs: Change highlighters' URL indexes from numbers to labels

docs/highlighters.md

@@ -3,19 +3,19 @@ zsh-syntax-highlighting / highlighters
 
 Syntax highlighting is done by pluggable highlighters:
 
-* `main` - the base highlighter, and the only one [active by default][1].
-* `brackets` - [matches brackets][2] and parenthesis.
-* `pattern` - matches [user-defined patterns][3].
-* `cursor` - matches [the cursor position][4].
-* `root` - highlights the whole command line [if the current user is root][5].
-* `line` - applied to [the whole command line][6].
-
-[1]: highlighters/main.md
-[2]: highlighters/brackets.md
-[3]: highlighters/pattern.md
-[4]: highlighters/cursor.md
-[5]: highlighters/root.md
-[6]: highlighters/line.md
+* `main` - the base highlighter, and the only one [active by default][main].
+* `brackets` - [matches brackets][brackets] and parenthesis.
+* `pattern` - matches [user-defined patterns][pattern].
+* `cursor` - matches [the cursor position][cursor].
+* `root` - highlights the whole command line [if the current user is root][root].
+* `line` - applied to [the whole command line][line].
+
+[main]: highlighters/main.md
+[brackets]: highlighters/brackets.md
+[pattern]: highlighters/pattern.md
+[cursor]: highlighters/cursor.md
+[root]: highlighters/root.md
+[line]: highlighters/line.md
 
 
 Highlighter-independent settings