title: Protobuff serialise System.Numerics.BigInteger
body: <p>The code:</p>
  
  <pre><code>[ProtoMember(11002)]
  public BigInteger StartInteger { get; private set; }
  </code></pre>
  
  <p>Throws the exception:</p>
  
  <pre><code>No serializer defined for type: System.Numerics.BigInteger
  </code></pre>
  
  <p>How can I make <code>StartInteger</code> serialisable?</p>