Make sure that Try .NET embed content degrades gracefully when Try .NET is unavailable

[jonsequitur]

When code is loaded using a Gist currently, if Try .NET becomes unavailable, then the code cannot be viewed in the embedding page. An approach such as using <pre> tags to embed code, and then making that code interactive using a script (#95), could allow for graceful degradation of the experience that preserves the usefulness of the overall document.