The templateSelection option was used in the demo, but was not shown in the example code.
This commit fixes it, so that copy&pasting works as expected.
This fixes some bugs that were present in the old Prettify highlighter
when there was a mix of JavaScript and HTML in the same code block. Now
with Rouge, the highlighter used by Jekyll, these cases are properly
handled and HTML no longer looks strange.
This does not convert all of the code blocks over, because there are
still some code blocks which double as the actual JavaScript code
powering the example that need to be migrated.
