Add "strip-links" parameter, addressing Issue 188

On Tumblr (and likely other CMS's), URLs, even in `<pre/>` blocks, get turned into links, as shown below:

![with mainline code](https://f.cloud.github.com/assets/1349578/295419/a44b1c78-948a-11e2-96bf-c3acfbb44fa2.png)

But, if you set my new `strip-links` parameter to `true`, it looks like this:

![with strip-links = true](https://f.cloud.github.com/assets/1349578/295422/58dcac38-948b-11e2-9f95-0ffda442857f.png)

The default value is `false`, so the change is opt-in only. This addresses [Issue 188](https://github.com/alexgorbatchev/SyntaxHighlighter/issues/188).