Cross-Site Scripting

I've picked up on the work started over at https://github.com/erusev/parsedown/pull/276 and rebased on erusev/master. Since this is rebased on master, I can't point at PR at naNuke/master without running into the merge conflicts that I've already resolved manually. I've implemented what I suggest...

List of changes and fixed issues in the .NET Framework 3.5 Service Pack 1

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