title: Should I include every header?
body: <p>Should I include every header even if it was included before? Or maybe I should avoid it when I can?
  For example. If I use <code>std::string</code> and <code>std::vector</code> in some file. If <code>&lt;string&gt;</code> included <code>&lt;vector&gt;</code> should I include only <code>&lt;string&gt;</code> or <code>&lt;string&gt;</code> and <code>&lt;vector&gt;</code>?</p>