title: System.Numerics.Vectors.Vector<T> is missing
body: <p>I'm studying examples of SIMD operations in C# and want to try some exapmles. I downloaded NuGet package <code>System.Numerics.Vectors v4.0</code>, and want to reproduce examples from the internet. But they doesn't work because this library doesn't contain class needed. Target framework is 4.6, but there is no <code>Vector&lt;T&gt;</code> for some reason, and I don't know why.</p>
  
  <p><img src="https://i.stack.imgur.com/3067n.png" alt="enter image description here"></p>
  
  <p>Maybe it was removed from API, but i didn't found any correlated info why they did it.</p>