Add tests and docs to unwind-blank feature

[juanjoDiaz]

This adds the missing tests and an example to the documentation for #285.

Also, it removes the trailing comma.
I like trailing commas ala air-bnb. However, we don't use them anywhere in the code base and I think that consistency is important.

[coveralls]

Coverage remained the same at 85.35% when pulling 6f12970 on juanjoDiaz:cleanup_unwind_blank into d97a668 on zemirco:master.