title: ReadOnlySequence<byte> parsing
body: <p>So i have started experimenting with Span for a message parsing code.
  Although the api looks easy to understand i cant seem to find any way to convert the slices to an value.
  For example i would want to convert an ReadOnlySequence to int.
  Sure i can call ToArray and use BitConverter but that would actually create a new array which is what i am trying to avoid.</p>
  
  <p>Here is example on how i get the slices</p>
  
  <pre><code>        var DHCP_OP = buffer.Slice(0, 1);          
          var DHCP_HTYPE = buffer.Slice(1, 1);
          var DHCP_HLEN = buffer.Slice(2, 1);
          var DHCP_HOPS = buffer.Slice(3, 1);
          var DHCP_XID = buffer.Slice(4, 4);
          var DHCP_SECS = buffer.Slice(8, 2);
          var DHCP_FLAGS = buffer.Slice(10, 2);
          var DHCP_CI_ADDR = buffer.Slice(12, 4);
          var DHCP_YI_ADDR = buffer.Slice(16, 4);
          var DHCP_SI_ADDR = buffer.Slice(20, 4);
          var DHCP_GI_ADDR = buffer.Slice(24, 4);
          var DHCP_CH_ADDR = buffer.Slice(28, 16);
          var DHCP_SNAME = buffer.Slice(44, 64);
          var DHCP_FILE = buffer.Slice(108, 128);
  </code></pre>
  
  <p>and this is how i potentially could convert to int </p>
  
  <pre><code>      var DHCP_OP = buffer.Slice(0, 1).ToArray();
        var integer = BitConverter.ToInt32(DHCP_OP, 0);
  </code></pre>
  
  <p>So what are the options here ? Have i missed something or ToArray is the only option?
  Thanks.</p>