Closes #1392.

In html content, marked allow `Inline-Level Grammar` but not `Block-Level Grammar`, so when I write following:
```
note:
* a
* b
* c
```
it become:
```html
<p><em> a
</em> b</p>
<ul>
<li>c</li>
</ul>
```
unbelievable!

Just using $ as delimiter in markdown document fails since the markdown
parser unknown to the dollar syntax will try to interpret underscores.
Putting the $ delimented formula in backticks will cause the markdown
parser to put the tex-code with the $ delimiters into a code block.
The texcode will then be unchanged. This patch allows for mathJax to
interpret and automagically display the tex-formulas.

by changing the tag before html is parsed and restoring it before markdown parsing

Compressed with `uglifyjs lib/marked.js --comments="/Copyright/" --mangle --compress`

Used Marked v0.3.3 as of chjj/marked@2b5802f258c5e23e48366f2377fbb4c807f47658

see https://github.com/hakimel/reveal.js/issues/929#issuecomment-80738837

It would be nice if we could define a custom notes.html file.

Actually, I'm used to compile my js files before releasing my app and, using selectors like `script[src$="notes.js"]`, doesn't work :(

So, what do you think about it?

add global flag back in for whitespace removal, without it most of the content in example.html does not work #682