Targetfile updating

When an asset name is updated using filerev, it's new name is stored in the summary object, but it is not updated in files that reference the updates asset. I added code that performs this functionality. It involves the user specifying an option 'targetFiles' to identify which files should be updated.

So, for example, if 'file.png' is updated to 'file.a0539763.png' and in the gruntfile it is specified that 'index.html' is a targetFile, any reference to file.png is updated to file.a0539763.png.