feat!: support only "-", "•" as listitem prefix

"+" and "*" have many false-positives and aren't commonly used as
a listitem prefix.

grammar.js

@@ -8,7 +8,7 @@
 // - Rules starting with underscore are hidden in the syntax tree.
 
 const _uppercase_word = /[A-Z0-9.()][-A-Z0-9.()_]+/;
-const _li_token = /[-*+•][ ]+/;
+const _li_token = /[-•][ ]+/;
 
 module.exports = grammar({
   name: 'help', // The actual language name is help
@@ -43,8 +43,8 @@ module.exports = grammar({
     )),
     word_noli: ($) => prec(1, choice(
       // Lines contained by line_li must not start with a listitem symbol.
-      token(prec(-1, /[^-*+•\n\t ][^\n\t ]*/)),
-      token(prec(-1, /[-*+•][^\n\t ]+/)),
+      token(prec(-1, /[^-•\n\t ][^\n\t ]*/)),
+      token(prec(-1, /[-•][^\n ]+/)),
       choice($._word_common),
     )),
 
@@ -74,6 +74,8 @@ module.exports = grammar({
       '|',
       // NOT listitem: "-" or "•" followed by tab.
       /[-•]\t/,
+      // NOT tag:
+      '*',
       // NOT argument:
       '{',
       '}',