fixed issues with \<pre\>, \<code\> and certain things following ```

**The issues fixed were:**

1. \\\<pre\>\\\</pre\\\> and \\\<code\\\>\\\</code\\\> would be recognized as code blocks despite being escaped.
2. Lines beginning with: \`\`\` {style=""} (a convention used at least by github and pandoc) aren't considered a **mkdCode** region, so the end region is seen as a start region, and everything in the document until the end of the next code block with a style region or the end of the document ends up being seen as a code block when it's supposed to be markdown or vice versa. I realize that this might not be standard markdown syntax (stated as a requirement in _CONTRIBUTING.md_), but if this is the case (and correct me if I'm wrong), I don't believe my change for this issue would match anything any differently in standard markdown.

Cheers!