Retag wheels automatically when fusing

[dunkmann00]

This is my attempt at a PR for #174.

This adds the ability to "retag" a universal2 fused wheel. When running delocate-fuse with this flag, it will update the filename and the dist-info file of the fused wheel to reflect that it is a universal2 wheel.

I didn't update the readme or add any tests yet. I wanted to first get feedback on whether or not this is the "retag" you had in mind.

Let me know what you think/if there is anything you would like changed!