Add snippet anchor

[SimonCropp]

New snippet rendering will be

<!-- snippet: MySnippetName -->
Some blurb about the below snippet
<a id='snippet-MySnippetName'/></a>
```
My Snippet Code
```
<sup>[snippet source](/relativeUrlToFile#L1-L11) / [anchor](#snippet-MySnippetName)</sup>
<!-- endsnippet -->

Note the anchor link that points back to the top of the snippet.

This enable people to deep link into specific snippets