docs: Change broken fg(1) links to fg(1p)

The fg(1) links in the readline docs have moved
from `http://man7.org/linux/man-pages/man1/fg.1.html`
to `http://man7.org/linux/man-pages/man1/fg.1p.html`.
It also modifies the regex for replacing man page links
in docs by allowing optional character after number.
eg: fg(1) and fg(1p) will both be now parsed and replaced.

Fixes: #11492

doc/api/readline.md

@@ -124,7 +124,7 @@ added: v0.7.5
 
 The `'SIGCONT'` event is emitted when a Node.js process previously moved into
 the background using `<ctrl>-Z` (i.e. `SIGTSTP`) is then brought back to the
-foreground using fg(1).
+foreground using fg(1p).
 
 If the `input` stream was paused *before* the `SIGTSTP` request, this event will
 not be emitted.
@@ -174,7 +174,7 @@ input, typically known as `SIGTSTP`. If there are no `SIGTSTP` event listeners
 registered when the `input` stream receives a `SIGTSTP`, the Node.js process
 will be sent to the background.
 
-When the program is resumed using fg(1), the `'pause'` and `SIGCONT` events
+When the program is resumed using fg(1p), the `'pause'` and `SIGCONT` events
 will be emitted. These can be used to resume the `input` stream.
 
 The `'pause'` and `'SIGCONT'` events will not be emitted if the `input` was

tools/doc/html.js

@@ -288,15 +288,15 @@ var BSD_ONLY_SYSCALLS = new Set(['lchmod']);
 // Returns modified text, with such refs replace with HTML links, for example
 // '<a href="http://man7.org/linux/man-pages/man2/open.2.html">open(2)</a>'
 function linkManPages(text) {
-  return text.replace(/ ([a-z.]+)\((\d)\)/gm, function(match, name, number) {
+  return text.replace(/ ([a-z.]+)\((\d)([a-z]?)\)/gm, function(match, name, number, optionalCharacter) {
     // name consists of lowercase letters, number is a single digit
-    var displayAs = name + '(' + number + ')';
+    var displayAs = name + '(' + number + optionalCharacter + ')';
     if (BSD_ONLY_SYSCALLS.has(name)) {
       return ' <a href="https://www.freebsd.org/cgi/man.cgi?query=' + name +
              '&sektion=' + number + '">' + displayAs + '</a>';
     } else {
       return ' <a href="http://man7.org/linux/man-pages/man' + number +
-             '/' + name + '.' + number + '.html">' + displayAs + '</a>';
+             '/' + name + '.' + (number + optionalCharacter) + '.html">' + displayAs + '</a>';
     }
   });
 }