Flexible performance tuning, use the inner html of inline content containers

I ran into a situation where inline mode was required and putting 100+ high quality images inside of hidden div tags would compete with other media loading on the page. In other words, this was not an appropriate situation to cache the full scale images before loading by putting them in a hidden div tag, they needed to be loaded on demand. To accomplish this I made the inline HTML containers script tags to prevent the image tag from being interpreted as HTML until it was needed. For example:
```html
			<script type="text/template" id="modal-node-44">
				<img src="http://38.media.tumblr.com/1168e5eb25c9f871d502945f5dd48f31/tumblr_mxs2sv5RwC1qzy7w4o1_500.jpg">
			</script> 
```

The problem is that the script tag itself would also end up in the modal content area resulting in what appeared to be an empty modal.  Changing one line in `jquery.colorbox.js`, colorbox now uses the inner HTML of the inline HTML container for the modal content. Not only does this give you cache control, ie. the flexibility of choosing if inline modal content is loaded on page load, it also results in what may be seen as a cleaner approach to when you do want content cached. If anything, it's less verbose.

```html
			<div style="display: none;">
				<div id="modal-node-44">
					<img src="http://38.media.tumblr.com/1168e5eb25c9f871d502945f5dd48f31/tumblr_mxs2sv5RwC1qzy7w4o1_500.jpg">
				</div> 
			</div>
```
vs.
```html
			<div style="display: none;" id="modal-node-44">
				<img src="http://38.media.tumblr.com/1168e5eb25c9f871d502945f5dd48f31/tumblr_mxs2sv5RwC1qzy7w4o1_500.jpg">
			</div>
```
@jackmoore I submit my pull request here for your consideration. I'm wondering what your thoughts are here on my strategy for cache control. If it is deemed a worthy one, I could roll this pull request as an optional `useInnerHtmlForInlineContainers` setting to make this backwards compatible.