Add option for alphabetic sorting

Adds `options.sort` to `docdown(options)`. If `options.sort` is `true`,
then the methods (and categories, if enabled) are sorted alphabetically
in the documentation. If `false`, then methods (and categories) are
ordered as they appear in source. Defaults to `true`.

Fixes: jdalton#3

index.js

@@ -23,6 +23,7 @@ function docdown(options) {
     'lang': 'js',
     'sort': true,
     'title': path.basename(options.path) + ' API documentation',
+    'sort': true,
     'toc': 'properties'
   });
 

lib/generator.js

@@ -267,7 +267,7 @@ function generateDoc(source, options) {
 
     // Sort categories and add special categories back.
     if (sortEntries) {
-      tocGroups.sort(util.compareNatural);
+    if (sortEntries) tocGroups.sort(util.compareNatural);
     }
     push.apply(tocGroups, catogoriesUsed);
   }
@@ -354,4 +354,4 @@ function generateDoc(source, options) {
   return docMarkdown.join('\n');
 }
 
-module.exports = generateDoc;
+module.exports = generateDoc;