title: Ecto Repo.get_by with multple 'or' clauses
body: <p>I am attempting use Ecto Repo.get_by with multiple clauses, and I'm having trouble finding syntax examples. I need to query where either or 2 fields in the DB match, so an 'or' condition between the clauses. I can't figure out if this is even possible. </p>
  
  <pre><code>Repo.get_by(User, [username: username, email: username], prefix: :accounts) 
  </code></pre>