Removed ArgResult in lib/docgen.dart and removed top level variables.

pkg/docgen/bin/docgen.dart

Index: pkg/docgen/bin/docgen.dart
diff --git a/pkg/docgen/bin/docgen.dart b/pkg/docgen/bin/docgen.dart
index df6ce632d55f20297103d3a7db5b599122fe06e3..6c6bbcca96c943f0dea85816cd20064a94f802b8 100644
--- a/pkg/docgen/bin/docgen.dart
+++ b/pkg/docgen/bin/docgen.dart
@@ -15,15 +15,27 @@ import '../lib/docgen.dart';
  */
 void main() {
   logger.onRecord.listen((record) => print(record.message));
-  var results = initArgParser().parse(new Options().arguments);
-  if (results['help']) return;  
-  docgen(results);
+  var results = _initArgParser().parse(new Options().arguments);
+  
+  var outputToYaml = results['yaml'] || results['output-format'] == 'yaml';
+  var outputToJson = results['json'] || results['output-format'] == 'json';
+  if (outputToYaml && outputToJson) {
+    throw new ArgumentError('Cannot have contradictory output flags.');
+  }
+  outputToYaml = outputToYaml || !outputToJson;
+  
+  docgen(results.rest, 
+      packageRoot: results['package-root'], 
+      outputToYaml: outputToYaml,  
+      includePrivate: results['include-private'], 
+      includeSdk: results['parse-sdk'] || results['include-sdk'], 
+      parseSdk: results['parse-sdk']);
 }
 
 /**
  * Creates parser for docgen command line arguments. 
  */
-ArgParser initArgParser() {
+ArgParser _initArgParser() {
   var parser = new ArgParser();
   parser.addFlag('help', abbr: 'h', 
       help: 'Prints help and usage information.', 
@@ -32,6 +44,7 @@ ArgParser initArgParser() {
         if (help) {
           logger.info(parser.getUsage());
           logger.info(USAGE);
+          exit(0);
         }
       });
   parser.addFlag('verbose', abbr: 'v',