title: What are buildOptions and preserveCompilationContext used for?
body: <p>I am playing with just released ASP.NET Core. I have created new project and I am looking at <code>project.json</code>. I'd like to know what is this part of configuration for:</p>
  
  <pre><code>"buildOptions": {
     "emitEntryPoint": true,
     "preserveCompilationContext": true
  }
  </code></pre>