Rev image filenames referenced in the main stylesheet or html files.

Closes:
* #3

I have tested this in Windows and it works. Perhaps this should be a option that can be enabled or disabled? Here it is anyways, I set up an example.


Any image file that exists on the server and is referenced within the HTML or CSS files gets revved.

## Example

Images that are referenced inside the following get revved:

* Main stylesheet.
* Any imported stylesheet within the main stylesheet.
* Any HTML file that is declared within the property file.pages or file.pages.default.include

*Images that have a path started with either ftp, http, https, // or data get skipped. Even if we would go through these they would be skipped as well because they don't exist on the server.*

index.html
------------
    index.html before:
        <img src="img/group.gif">
        <div style="background:url(img/heart.gif);"></div>
        <a href="img/invalid.gif">
            <img src="img/invalid.gif">
        </a>

    index.html after:
        <img src="img/399ec93098c4e56a30c3.gif">
        <div style="background:url(img/f45d94f826087653264f.gif);"></div>
        <a href="img/2825ab67e4f7c50e8ab7.gif">
            <img src="img/2825ab67e4f7c50e8ab7.gif">
        </a>

main.css
------------
    main.css before:
        .alert { background: url(../img/alert.gif); }
        .arrow { background: url(../img/arrow.png); }

    main.css after:
        .alert { background:url(../img/11f7edbe9e04d0a61078.gif); }
        .arrow { background:url(../img/0658353dbcad56bbc535.png); }