Unpaired Backticks (`) break syntax highlighting.

[bcj]

Unpaired backticks (```) in a code block causes highlighting to break until an additional triple backtick is encountered.

This issue body will demonstrate the behavior when the raw text is copied into sublime.

Paired backticks:

> echo '`works`'
`works`

Unpaired backticks:

> echo '`'
`

This text is still being sh syntax highlighted. So is this python code:

> print('still sh')
still sh

To escape sh, an additional triple backtick is required:

_This_ text is markdown syntax highlighted.

```python
> print('python syntax')
python syntax

Here is a copyable version of that body:

Paired backticks:

```sh
> echo '`works`'
`works`

Unpaired backticks:

> echo '`'
`

This text is still being sh syntax highlighted. So is this python code:

> print('still sh')
still sh

To escape sh, an additional triple backtick is required:

_This_ text is markdown syntax highlighted.

```python
> print('python syntax')
python syntax

[jonschlinkert]

Is that related to this library or sublime text?

[bcj]

This is specific to this library. Sublime's built-in Markdown syntax highlighting will render this example correctly (albeit, without syntax highlighting for code blocks)

[jonschlinkert]

punting to https://github.com/jonschlinkert/sublime-markdown-extended/issues/142