RAR File List Metadata

This is a first pass at implementing something that would cover issue #7.  I've created a new ```listFilesWithMetadata``` method which contains more of the header data (packed and unpacked file size, archive name, crc, etc) which is now contained in a new ```URKFileInfo``` class.  

I've kept the original method for backwards compatibility.

@abbeycode, let me know what you think.  This is very preliminary and I'm not 100% certain all the fields I'm mapping in ```URKFileInfo``` are correct.  The documentation isn't that great.  I mostly went off [RARLabs Rar 5.0 spec](http://www.rarlab.com/technote.htm#filehead) and the [forensics wiki](http://www.forensicswiki.org/wiki/RAR).