Add support for separators.

lib/src/usage.dart

Index: lib/src/usage.dart
diff --git a/lib/src/usage.dart b/lib/src/usage.dart
index 11be54b38983900ea14ddf0c9223bcb20b2a6923..162dcbde634ac50f4dddc293c61b5cad633627e5 100644
--- a/lib/src/usage.dart
+++ b/lib/src/usage.dart
@@ -62,8 +62,17 @@ class Usage {
 
     calculateColumnWidths();
 
-    args.options.forEach((name, option) {
-      if (option.hide) return;
+    for (var optionOrSeparator in args.optionsAndSeparators) {
+      if (optionOrSeparator is String) {
+        // Ensure that there's always a blank line before a separator.
+        if (buffer.isNotEmpty) buffer.write("\n\n");
+        buffer.write(optionOrSeparator);
+        newlinesNeeded = 1;
+        continue;
+      }
+
+      var option = optionOrSeparator;

[Bob Nystrom, 2015/05/21 16:43:16]

Do you need an "as Option" here?

[nweiz, 2015/05/21 19:22:27]

The analyzer infers it as dynamic, so it doesn't produce any warnings. That also
means it won't warn about misuse, though; would you prefer that I add it?

[Bob Nystrom, 2015/05/21 19:42:27]

Yeah, I think so.

[nweiz, 2015/05/21 19:52:37]

Done.

+      if (option.hide) continue;
 
       write(0, getAbbreviation(option));
       write(1, getLongOption(option));
@@ -94,7 +103,7 @@ class Usage {
       // blank line after it. This gives space where it's useful while still
       // keeping simple one-line options clumped together.
       if (numHelpLines > 1) newline();
-    });
+    }
 
     return buffer.toString();
   }