title: Convert array (or vector) of u16 (or u32, u64) to array of u8
body: <p>I have no problem to do it for <a href="https://stackoverflow.com/questions/53314005/how-can-i-convert-the-lower-upper-8-bits-of-a-u16-to-a-u8-in-rust">u16 to u8</a> using bit shifts and cast but how could I do it with an array of u16? Even ideally I would prefer to convert directly from vec to [u8]. What would be the most elegant way to do it?</p>
  <pre class="lang-rs prettyprint-override"><code>&amp;my_vector[..] // my vector converted to [u16] but I need [u8]
  </code></pre>