Apologies for the bikeshed, but I have a few comments about the API that might be worth considering before a 1.0 release:

• When a trait represents an action, it is generally named imperatively (Display,Read,Write,Hash, etc.). For least surprise,UnicodeNormalization could be namedUnicodeNormalize instead, or perhaps evenNormalize, to avoid repeating the module name.
• The method namesnfd,nfkd,nfc, andnfkc have no intrinsic meaning, which makes it hard to know what they do in isolation, outside of the context of theUnicodeNormalization docs. Even for a person who is aware of the concept of Unicode normalization, it might not be clear what a line likelet c = s.nfc().collect::<String>(); does, without first having seen the documentation, or an explanatory comment. Something likenormalize_form_c would at least suggest that some kind of normalization is going on.