title: Rails: Add assets to manifest from within gem
body: <p>Is there a way to add assets (JS) to the manifest from within a gem with explicitly referencing them in the manifest file?</p>
  
  <p>The assets are in the correct place and picked–up just fine, but I'd like to get around asking the user to manually add e.g. </p>
  
  <pre><code>//= require 'my_asset_path'
  </code></pre>
  
  <p>to their manifest file.</p>
  
  <p>I'd also like to avoid the approach describe here since it seems a bit brittle: 
  <a href="http://bibwild.wordpress.com/2011/09/20/design-for-including-rails-engine-assets-into-pipeline-manifest/" rel="nofollow noreferrer">http://bibwild.wordpress.com/2011/09/20/design-for-including-rails-engine-assets-into-pipeline-manifest/</a>  </p>