title: What is a conventional place to keep custom Exception definitions in a rails project?
body: <p>When making one's own custom exceptions like</p>
  
  <pre><code>class ThingExploded &lt; StandardError; end
  class ThingIsMissing &lt; StandardError; end
  </code></pre>
  
  <p>Where is a good place to keep these? I was considering <strong>lib/exceptions.rb</strong>… and also pondering if it would be more appropriate to somehow put them closer to the code that uses them.</p>